Fundamentals of Aerospace Medicine

FOURTH EDITION

FUNDAMENTALS OF AEROSPACE MEDICINE EDITORS

Jeffrey R. Davis, MD, MS

Robert Johnson, MD, MPH, MBA

Professor Preventive Medicine and Community Health The University of Texas Medical Branch Galveston, Texas

Associate Professor Preventive Medicine and Community Health The University of Texas Medical Branch; Staff Physician Aviation Medical Center University of Texas Medical Branch University Hospitals Galveston, Texas

Jan Stepanek, MD, MPH Assistant Professor Medical Director Aerospace Medicine Program Division of Preventive, Occupational and Aerospace Medicine Department of Internal Medicine Mayo Clinic Scottsdale, Arizona; Assistant Professor Preventive Medicine and Community Health The University of Texas Medical Branch Galveston, Texas

Jennifer A. Fogarty, PhD Adjunct Assistant Professor Preventive Medicine and Community Health The University of Texas Medical Branch Galveston, Texas; Biomedical Risk Coordinator Space Medicine Division NASA Houston, Texas

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Library of Congress Cataloging-in-Publication Data Fundamentals of aerospace medicine / editors, Jeffrey R. Davis . . . [et al.].—4th ed. p. ; cm. Includes bibliographical references and index. ISBN 978-0-7817-7466-6 1. Aviation medicine. 2. Space medicine. I. Davis, Jeffrey R. [DNLM: 1. Aerospace Medicine. 2. Space Flight. WD 700 F981 2008] RC1062.F86 2008 616.9
8021—dc22 2008003374 Care has been taken to confirm the accuracy of the information presented and to describe generally accepted practices. However, the authors, editors, and publisher are not responsible for errors or omissions or for any consequences from application of the information in this book and make no warranty, expressed or implied, with respect to the currency, completeness, or accuracy of the contents of the publication. Application of this information in a particular situation remains the professional responsibility of the practitioner. The authors, editors, and publisher have exerted every effort to ensure that drug selection and dosage set forth in this text are in accordance with current recommendations and practice at the time of publication. However, in view of ongoing research, changes in government regulations, and the constant flow of information relating to drug therapy and drug reactions, the reader is urged to check the package insert for each drug for any change in indications and dosage and for added warnings and precautions. This is particularly important when the recommended agent is a new or infrequently employed drug. Some drugs and medical devices presented in this publication have Food and Drug Administration (FDA) clearance for limited use in restricted research settings. It is the responsibility of the health care provider to ascertain the FDA status of each drug or device planned for use in their clinical practice. To purchase additional copies of this book, call our customer service department at (800) 638-3030 or fax orders to (301) 223-2320. International customers should call (301) 223-2300. Visit Lippincott Williams & Wilkins on the Internet: at www.LWW.com. Lippincott Williams & Wilkins customer service representatives are available from 8:30 AM to 6:00 PM, EST. 10 9 8 7 6 5 4 3 2 1

FOREWORD

Unlike most Forewords, I have elected to commence by going backward. For the benefit of the reader of this fourth edition of ‘‘Fundamentals’’ I begin with a very brief review of this texts’ progenitors. The foundation for this series of textbooks was laid by Dr. Louis Bauer in 1926 when he published the first volume on this topic in the United States—Aviation Medicine. Dr. Bauer also played an important role in the development of Civil Aviation as well as the specialty of Aerospace Medicine and became a president of the American Medical Association. In 1939, building on the foundation established by Dr. Bauer, Dr. Harry Armstrong authored his first edition of The Principles and Practice of Aviation Medicine. As Dr. Armstrong’s career progressed in the Army Air Corp: from laboratory commander, to General Officer, to Commander of the School of Aviation Medicine culminating as the Air Force Surgeon General—his textbook progressed from the second to the third editions. His next book carried a new title in 1961 reflecting the growing interest of ‘‘man in space’’ and was edited by Dr. Armstrong as he was joined by other contributors to Aerospace Medicine. The second edition, the mantle for editing which fell to Dr. Hugh Randel, a flight surgeon and Preventive Medicine Specialist, was published in 1971. In 1980 as I departed the Armstrong Aerospace Medical Research Laboratory at Wright-Patterson to take command of the USAF School of Aerospace Medicine, a new edition was needed in response to the new research and developments in the field that had occurred during the past decade since the last textbook had appeared. Unfortunately, it was not possible to use the title introduced by Dr. Armstrong due to issues of clearing the copyright restrictions. Although Dr. Randel had visions of a third edition, he found he had neither the time nor the resources to proceed. At this point, it became necessary to change both the publisher and the title if the book was to continue, and I introduced Fundamentals of Aerospace Medicine and proceeded to identify other contributors who willingly joined in writing the chapters. This textbook was published in 1985 under my editorship. In 1996, the second edition

followed with the third in 2002 jointly edited with Dr. Jeff Davis. Now we go forward to this the fourth edition; time and circumstance combined with age and wisdom to place the challenge of editorship into younger and willing hands to move forward with the task. Dr. Davis had been requested to assist as co-editor of the third edition with the commitment to take on the responsibility of the fourth edition as I withdrew. This text is now in the hands of Dr. Davis and his co-editors. The reader will quickly note that while military topics fade they are replaced with more contributions found on space medicine with commercial and general aviation holding their own. This reflects the changing allocation of research commitments in the United States. From the first edition of Aviation Medicine through the current fourth edition of ‘‘Fundamentals’’ the goal has not changed—to provide information on the physiology of flight, the hazards of flight, and the selection and health maintenance of those who fly and those who facilitate such activities. New to this edition are chapters on Radiation, Toxicology, Emerging Infectious Disease, Dental, and Women’s Health. The new section on the future discusses the governments’ role in Aerospace and Commercial space activities. This text is for the most part written from the perspective of the United States. This is not intended to be an international tome but it is anticipated that as with the prior editions other nations will find it useful. The audience has remained unaltered over time—physicians, physiologists, researchers, residents, and interested readers on the challenges to people in flight—whether in the terrestrial environment or the vastness of space. This edition proves the merits of my decision to leave the stage for the next generation, and I thank readers for the kind words offered to the contributors and me for our best efforts.

Roy L. DeHart, MD, MPH, MS Colonel and Chief Flight Surgeon, USAF (Ret) Professor and Medical Director, Corporate Health Services Vanderbilt University Medical Center

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FOREWORD TO THIRD EDITION

This third edition of the already classic textbook Fundamentals Of Aerospace Medicine reflects and covers in detail contemporary trends in the evolution of a fascinating medical discipline, which in many areas of the world has achieved the level of a postgraduate university specialty. Aviation medicine (later on, by natural extension, Aerospace Medicine) started as an indispensable response to a need to regulate the presence of humankind in aviation in relation to operational safety. More recently its scope has been broadened globally by giving emphasis to its preventive aspect; greater attention is additionally given to all occupants of air and spacecraft, including passengers and space tourists. The magnitude of global air transportation of healthy and less well passengers established the need to have a continuous update of knowledge of operational and environmental conditions (potentially) affecting humans. Such need is of paramount importance and this edition includes the most current information available in contemporary Aerospace Medicine. Humans have adjusted their biological systems to life at or near sea level where they function at a given barometric pressure and a given partial pressure of oxygen with a normal hemoglobin range. Departure from this environment to altitude brings about the need to have adaptation mechanisms, which encompass ventilatory, circulatory and hematological adjustments over time. Exposure to altitude conditions by aviation is almost immediate and does not allow the time for adaptation mechanism to appear, therefore technological aids are indispensable and as such, a classical example is given by cabin pressurization systems. Proper interaction of humans, machines and environments is needed to achieve an optimum level of Operational Safety. Emphasizing again the need for proper interaction, we should remember that humans are necessary for the design, operation and maintenance of aircraft. Every year, almost one quarter of the world’s population travel by air on scheduled flights with an optimum level of safety compared to other means of mass transportation. In trying to satisfy the needs of the traveling public, experts are working hard in providing solutions to problems, or even better in preventing the appearance of those problems. Our specialty, a significant contributor to such level of safety, has seen a significant evolution of well defined and documented periods: its beginnings were empirical and were followed by observational, experimental, human factors and ergonomic stages. More recently the legal implications attracted the attention of the experts and, in this respect, more studies are being conducted in jurisprudence and ethics before an aeromedical decision takes place.

Over the years, aviation and medical authorities realized that research was needed and studies began to assess human performance and limitations related to aerospace environments and a need arose for a more precise definition of the objective of the specialty. In relation to civil aviation, most of these studies were conducted at national levels; it soon became apparent that to achieve proper international standardization, medical requirements for aviation duties had to be adopted by an International Organization of the United Nations System, namely the International Civil Aviation Organization. These requirements were incorporated in Annex 1 to the Chicago Convention and they include physical, mental, hearing, visual and color perception requirements. As a result of these standards and recommendations and their evaluation in the context of flight safety, it became indispensable to further study in detail the proper assessment of human performance, limitations and the consequences of exceeding those limitations. Paraphrasing two sentences of General Howard W. Unger’s foreword to the first edition of this textbook, it is worthwhile to emphasize that the specialty of Aerospace Medicine reflects a dynamic and progressive nature and that the need to openly share the wealth of information gathered is readily apparent. Several definitions of Aerospace Medicine are available to readers; it seems indispensable to emphasize that, as far as crew members are concerned, it should be viewed as a multidisciplinary specialty related to valid mental and physical requirements in response to realistic operational needs to properly perform duties with an optimum level of safety. Related to passengers, clinical and environmental aspects are significant in order to achieve a good level of safety, health, comfort and well being. Summarizing, it is indispensable for practitioners of Aerospace Medicine to continuously assess the adequate interaction needed between humans, machines and environments. Therefore, this edition of Fundamentals of Aerospace Medicine provides information and references useful to the medical examiners as well as to specialists in all aspects of the discipline. The wealth of information presented in this third edition allows practitioners, specialists and researchers to acquire it in a very well organized presentation. Such acquisition will allow us to have optimum exchanges of views and to perform duties in line with the requirements.

Silvio Finkelstein, MD, MSc Former Senior Official, International Civil Aviation Organization Past President, International Academy of Aviation and Space Medicine

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FOREWORD TO SECOND EDITION

In introducing this impressive volume, I believe it most important to begin with a definition of the subject. Aerospace medicine is that specialty area of medicine concerned with the determination and maintenance of the health, safety, and performance of those who fly in the air or in space. This specialty is necessary because such flight subjects humans, with their earth-bound anatomy, physiology and psychology, to the hostile environment of air and space. Humans must adapt to or be protected from the changes in total environment pressure, reduced partial pressures of vital gasses, accelerative forces of flight, and changes in gravitational forces, to name just a few of the hazards encountered in flight. Historically, the early balloon flights in the late 1700’s produced reports of physical effects on the humans engaged in such ascents, but they were treated as interesting physiological observations. The advent of powered flight 92 years later by the Wright brothers on December 17, 1903 and then human spaceflight by Gagarin on April 12, 1961 revealed additional effects and potential obstacles to human performance in this new environment. However, these obstacles were viewed as challenges to be solved by those individuals supporting the explorers of these environments. They learned that the environments of air and space were a continuum and that basic physiologic fundamentals applied throughout this continuum. It is these environmental and vehicular stresses upon those who fly that are of ultimate concern to the aerospace medicine specialist. The specialty area of aerospace medicine is young compared to some other medical specialties. Even though physicians had supported those who flew from the beginning, the specialty was not recognized until 1953. Though relatively young, aerospace medical research and extensive operational experience has been accumulated and well documented. These dates are in numerous scientific journals, reports, and books. Specialized knowledge in many medical as well as nonmedical areas is required of the practitioner of aerospace medicine. The medical specialties of otolaryngology, ophthalmology, cardiology, neurology, psychiatry/psychology, and pathology are of particular importance. The human cannot be separated from the vehicle, therefore certain engineering principles are also important. The total support of those who fly becomes a team effort. The aerospace medicine specialist must be able to communicate with other specialists. He or she must be able to gather all of this information and evaluate its impact on the health status

of the pilot, relate this to the flying environment, and render a decision regarding fitness for flying. Therefore, the Fundamentals of Aerospace Medicine must cover a large amount of information. Aerospace medicine is of necessity very dynamic. It must keep pace with the ever-increasing technology of both medicine and aviation. Increases in fighter aircraft capabilities have forced a re-evaluation of a physiologic problem once thought to be solved. Current social assaults on the necessity of physical standards for those who fly have even forced a re-evaluation of medical standards. Aircraft are getting larger, and faster, and more and more people are flying. Such dynamic changes indicated the necessity for a current, comprehensive text. Dr. DeHart built upon the efforts of his predecessors, such as General Harry Armstrong, in gathering material for the first edition of Fundamentals of Aerospace Medicine. In the second edition, he has assembled the aid of respected authorities in their individual areas to add new chapter, update others with recent data and completely rewrite others. We must understand our past if we are not to repeat the errors of the past. The section ‘‘Aerospace Medicine in Perspective’’ covers some of this important history very well. The sections ‘‘Physiology of the Flight Environment,’’ ‘‘Clinical Practice of Aerospace Medicine’’ and ‘‘Operational Aerospace Medicine,’’ have chapters providing fundamentals with basic references. The section ‘‘Impact of the Aerospace Industry on Community Health’’ includes a chapter concerning transmission of disease by aircraft with current concerns about an old and nearly forgotten nemesis, tuberculosis. Fundamentals revisited again. New chapters have appropriately been added: ‘‘Thermal Stress,’’ ‘‘International Aviation Medicine’’ and ‘‘Management of Human Resources in Air Transport Operations.’’ It is the rare individual today who does not have some contact with the aviation environment in some manner. All physicians should have some basic knowledge of aerospace medical problems they or their patients might experience, as well as understand the breadth of knowledge possessed by the specialist in aerospace medicine. This text can serve as the basis of this knowledge for the general physician, the aerospace medicine specialist, the student, or anyone dealing with the medical support of military, general, or airline aviation, spaceflight, or the aerospace industry. It has been my privilege in 45 years of practice in Aerospace Medicine to participate in the Air Force, NASA,

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FOREWORD TO SECOND EDITION

and civilian areas. I congratulate Dr. DeHart and his authors for their excellent coverage of all these areas. If we adhere to the fundamentals and provide proper aerospace medical support, the human will continue to be able to adapt to zero gravity and re-adapt to earth’s gravity with ever longer sojourns in space. I believe we will see many of earth’s inhabitants experiencing spaceflight and even one day living in far flung space stations and colonies. The fundamentals will be the basic knowledge and the stepping stones making such progress possible. This knowledge must be used by the planners, designers, operators, and participants in

achieving safe flight. This volume makes that knowledge available.

Charles A. Berry, MD, MPH President, Preventive & Aerospace Medicine Consultants, P.A. Past President, Aerospace Medical Association Past President, International Academy of Aviation and Space Medicine Past President, University of Texas Health Science Center in Houston, Texas Former Director of Life Sciences—NASA

FOREWORD TO FIRST EDITION

This textbook reflects the dynamic and progressive nature of the specialty of aerospace medicine. The aviation industry has been explosive in development since the early 1900s, and the rapid advances in powered flight in military and civilian aviation have demanded the development of parallel medical systems to serve those who fly. The technologic advances that have occurred and continue to occur make it possible to move crews, passengers, troops, patients, and cargo far beyond all earlier expectations of time, size, weight, and distance. Although aviation has proven to be an important and increasingly rapid mode of transportation, it also has provided new methods of warfare and manned exploration beyond our planet. Over the years, as the aviation industry grew, the stresses associated with flight, such as acceleration, speed, and altitude, became increasingly apparent. Historic events resulting from the progressive expansion of the flight environment were steadily being catalogued. The necessity for research to study and explore the physiologic effects imposed on man were recognized and vigorously pursued. Although research into the effects of unpowered balloon flights was important, the frequency and magnitude of the stresses associated with powered flight increased the urgency and sophistication of research efforts. World War I provided the impetus for concerted educational and investigative efforts in the field of aviation medicine. Early in that war, human factors problems were strongly suspected as being the cause of many aircraft accidents and deaths. A school to train physicians to care for flyers and a medical research laboratory to consider urgent problems were established by the United States Air Service at Hazelhurst Field, Mineola, New York in 1917. Initial efforts to reduce the number of accidents and the loss of human life centered on good health and the application of more rigid physical standards for pilots and other aircrew members. The first class of ‘‘flight surgeons’’ graduated in 1918. A precipitous decrease in accidents and deaths was the direct result of these dedicated efforts. Since that time, flight surgeons have been intimately associated with flyers and their health and safety. As the list of medical responsibilities expanded, the industrial hygiene aspects of the developing industry included ground operations as well as the aerial mission. The school and laboratory at Hazelhurst Field

moved a number of times and in 1959 finally arrived at its present location at Brooks Air Force Base, San Antonio, Texas. The institution is now known as the United States Air Force School of Aerospace Medicine. Almost from the beginning of aviation medicine as a career field, it became apparent that a team effort was necessary so that an organized, multidisciplinary approach could be best applied to the problems associated with flight. Physicians, physiologists, psychologists, veterinarians, nurses, dentists, and other scientists covering many diverse skills and interests now contribute much time and effort to the men and women associated with flying. Although much of the emphasis initially was of a military nature, the civilian aspects of aviation grew by leaps and bounds, and today there is a dedicated, cooperative, worldwide military-civilian career field. Additional schools and laboratories are now devoted to the collection of scientific data and the dissemination of vital information. Typical of those involved in aviation or aerospace medicine has been the need and response to share openly the wealth of information being gathered. The complex and diverse data have been discussed by medical scientists of many nations at meetings and conferences. Periodicals and textbooks also have been very helpful in documenting and disseminating the knowledge that has accumulated. This text is a collection of the literary contributions of more than 40 authors representing the broad spectrum of aerospace medicine. Each contributor is a recognized expert among the many who practice within the specialty. These contributors are continuing a tradition begun over 50 years ago by Dr. Louis H. Bauer, who laid the first foundation stones with his text Aviation Medicine. Dr. Bauer’s work has been expanded by the contributions of Dr. Harry Armstrong and, most recently by Dr. Hugh W. Randal. Thus, this text holds to the tradition of enumerating the basic principles of the challenging field of aerospace medicine. This book will be both a practical text for the student and most valuable reference source for the practitioner of aerospace medicine.

Howard W. Unger, MD Major General, USAF, MC (retired) Past President of the Aerospace Medical Association Former Trustee of the American Board of Preventive Medicine

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P R E FA C E

Twenty-five years ago, it was decided to revive the tradition of Dr. Armstrong and edit a new textbook for the discipline of aerospace medicine. This fourth edition of Fundamentals of Aerospace Medicine continues the legacy of Dr. Roy DeHart who had the vision to develop this textbook many years ago. We are indebted to his many years of service and volunteer hours for the first three editions, and to his foresight to recruit a new editor for the third edition. Dr. Roy DeHart trained a new generation of editors, and the field will always be indebted to him for his selfless service. Three new section editors were added for this edition, and the efforts of Dr. Robert Johnson, Dr. Jan Stepanek, and Dr. Jennifer Fogarty were critical to the scope and timeliness of this text. There are many returning contributors from the third edition, as well as many new chapters and new contributors. This fourth edition reflects the tremendous pace of change in that two chapters are devoted to the future at the dawn of the commercial space flight industry. In the last 25 years, many changes have occurred in spaceflight and the pace of change has accelerated. The Space Shuttle first flew in 1981 and its planned retirement is on the horizon for 2010. The Mir Space Station was deorbited and replaced by the International Space Station (ISS) with the active participation by five international partners including the US, Russia, Japan, Canada, and the European Space Agency. Since the third edition, a second Space Shuttle accident resulted in the loss of Columbia and her crew of seven; the ISS was sustained using Russian Soyuz and Progress launches; and the first teacher in space flew completing the journey from the Challenger accident. Space Flight Participants pay to visit the ISS, and commercial space firms emerged after Space Ship One won the Ansari X-Prize. Various firms plan both suborbital and orbital space flights. Aerospace medicine practitioners of tomorrow may conduct medical exams for many interested passengers. Commercial aviation continues to expand with the first flights of long-range, fuel-efficient aircraft substantially built from composite materials. Large aircraft have flown capable of carrying 550+ passengers. Both new types of aircraft may enter service in 2008. These new aircraft, and the development of a global economy and travel, increase the potential for transmitting disease quickly around the Earth. New challenges to global public health are recognized by the international aviation authorities with sustained planning

efforts. In the US, the sport pilot certificate may stimulate the general aviation industry. Military aviation continues to be driven by speed, agility, and survivability. New aircraft with vectored thrust provide variable acceleration environments with new challenges to human performance. The need to adapt to the ever increasing stressors of flight has forced scientists and aviation system designers to be ever more innovative in protecting the combat pilot. Chapters in this edition address not only advances in crew systems protection but issues of human factors in flight operational environments. Unmanned Aerial Vehicles are now commonplace and the unique challenges of these flights are addressed in the chapter of human factors. The goal of the contributors to this edition is unchanged from a generation ago when the first edition was prepared for those physicians providing professional care and advice to general aviation pilots, for the specialist in aerospace medicine supporting the airline industry, the Department of Defense and the National Aeronautics and Space Administration, and now the emerging commercial space flight industry. The text is intended for students, residents, and perhaps many medical practitioners that may become more involved with global public health issues as well as medical exams for commercial space flight. The text is not intended to be a treatise on every subject introduced but rather a general review of the major topics that comprise the practice of aerospace medicine. The interested reader is provided with suggested readings and references to continue learning beyond the scope of this text. The reader will find many new chapters in this edition including chapters devoted to toxicology, radiation, dental, women’s health, unique aircraft, and commercial space flight. Substantial rewrites have been undertaken of many of the chapters from the third edition making this a substantially different text from the third edition. The pace of change is so great that planning is already underway for techniques to make new information available as soon as possible to the practitioner. As has been the case in the three preceding editions, proceeds from this text will be distributed to schools and scholarship programs, nationally and internationally, that educate and train physicians in the field of aerospace medicine.

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ACKNOWLEDGMENTS

As I mentioned in the preface, the current generation of practitioners of aerospace medicine owe a debt of gratitude to Dr. Roy DeHart who had the vision and determination to initiate Fundamentals of Aerospace Medicine some twentyfive years ago. I owe Dr. DeHart a heartfelt thank-you for allowing me to become an editor of the third edition, and to learn from him the complex process of assembling a text from content to contributors. Dr. DeHart not only revived this textbook with the first edition, but also insured its future by providing for new editors. His legacy to the field of aerospace medicine has many components, but this textbook may be the most significant in perpetuating the field. To Dr. Roy DeHart, thank you from the entire aerospace medicine community. For the fourth edition, I too brought new editors to the textbook. We decided to divide the book into sections of physiology, clinical aerospace medicine, and operations, and I chose a section editor for each. I am indebted to the hard work and many hours that these new editors contributed, Dr. Jennifer Fogarty (physiology), Dr. Jan Stepanek (clinical aerospace medicine), and Dr. Robert Johnson (operations). Dr. Bob Johnson also helped with the logistics of the textbook, organizing conference calls and notes to authors. Ms. Diane Ellison at the University of Texas Medical Branch also helped with many of the textbook conference calls, letters, e-mails, and phone calls while preparing the book. This textbook was truly a team effort, and they all put forth an outstanding effort and countless hours of time in editing and assembling this text. I want to recognize the contributors who are the authors who wrote this volume. Without their technical expertise, willingness to volunteer many hours of research, writing and revisions, this textbook would not exist. As a community of aerospace medicine practitioners, we owe a debt of gratitude to these authors without whom the underlying research, clinical evaluations, and operational experience would not exist to be able to sustain the field. In all aspects of practice, in operations, research, clinical medicine, and teaching, there are many competing demands for time, and less recognition

of the value of an academic effort to one’s home organization. So to the contributors and all of their outstanding technical contributions and volunteer efforts, one last grateful thankyou. There is a great deal of new material in this textbook as rapid developments are now occurring in aerospace. New opportunities are emerging in suborbital and orbital commercial space flight, and there are plans for commercial flights to the moon. These new developments should produce new practice opportunities for the aerospace medicine practitioner, and the future is as bright as perhaps at any time in the history of the field. By the time of the fifth edition, I hope we can look back on the successful flight of hundreds if not thousands of space flight participants on suborbital and orbital flights. It has been a pleasure to work with the Lippincott Williams & Wilkins staff, and the assistance of Ms. Kerry Barrett, Senior Managing Editor, was invaluable to the success of this edition. She was always available for sound advice, by email or phone, and would provide timely assistance to the editors and contributors. She also saw the value of the timing of this fourth edition with the rapid changes in aerospace including long-range and large commercial aircraft, global public health issues, the expansion of government space programs to include space flight participants, the emergence of an exploration program, and the rapid development of the commercial space flight industry. As Dr. DeHart noted in the third edition, Williams and Wilkins was the publisher of the original aviation medicine text, edited by Dr. Harry G. Armstrong, and the tradition most definitely continues. To you the next generation of practitioners, I hope this text gives you the foundation for success in aerospace medicine, and encourages you to become the next generation of practitioners, researchers, and teachers essential to the success of this field. I hope you enjoy the field as much as I have, and find the time to pass along your expertise to the next generation.

Jeffrey R. Davis

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CONTRIBUTORS

Richard Allnutt, MD, MPH, MS(EE) Biodynamic Research Corporation San Antonio, Texas Arnold A. Angelici, Jr., MD, MS Occupational Medicine Federal Aviation Administration Civil Aerospace Medical Institute Oklahoma City, Oklahoma ˜ Melchor J. Antunano, MD, MS Clinical Associate Professor Department of Preventive Medicine and Community Health University of Texas Medical Branch Galveston, Texas; Director Civil Aerospace Medical Institute Federal Aviation Administration Oklahoma City, Oklahoma Michael Bagshaw, MB, FFOM, DAvMed Program Director Aviation Medicine School of Biomedical & Health Sciences King’s College London Guy’s Campus London, UK Denise L. Baisden, MD, MS Assistant Regional Flight Surgeon Southwest Region Federal Aviation Administration Oklahoma City, Oklahoma

Stephen A. Bernstein, MD, MPH, FAAFP, COL, MC, SFS Director, US Army Aeromedical Activity US Army Enterprise, Alabama

Paula A. Corrigan, MD Branch Chief Department of Internal Medicine Aeromedical Consult Service USAF School of Aerospace Medicine Brooks City Base, Texas

James W. Brinkley, BS Former Director Human Effectiveness Directorate Air Force Research Laboratory Wright-Patterson Air Force Base, Ohio

Francis A. Cucinotta, MD Chief Scientist NASA Space Radiation Program Lyndon B. Johnson Space Center Houston, Texas

Stephen L. Carpenter, MD Medical Officer, Aerospace Medical Certification Division Federal Aviation Administration Oklahoma City, Oklahoma John W. Castellani, MD Research Physiologist Thermal and Mountain Medicine USARIEM Natick, Massachusetts Samuel N. Cheuvront, MD Research Physiologist Thermal and Mountain Medicine Division U.S. Army Research Institute of Environmental Medicine Natick, Massachusetts

Robert D. Banks, BEng, MD Principal Consultant Biodynamic Research Corporation San Antonio, Texas

Thomas F. Clarke, MD, MPH Director General Preventive Medicine Residency USAF School of Aerospace Medicine Brooks City Base, Texas

Michael R. Barratt, MD, MS Physician/Astronaut Johnson Space Center National Aeronautics and Space Administration Houston, Texas

Curtiss B. Cook, MD, FACP Lieutenant Colonel Professor of Medicine, Division of Endocrinology Mayo Clinic College of Medicine Scottsdale, Arizona

Jeffrey R. Davis, MD, MS Professor, Preventive Medicine and Community Health University of Texas Medical Branch Galveston, Texas Roy L. DeHart, MD, MS, MPH Professor and Director Vanderbilt Center for Occupational and Environmental Medicine Nashville, Tennessee J. Robert Dille, MD, MIH Consultant in Aerospace Medicine Norman, Oklahoma David F. Dinges, PhD Professor and Chief Division of Sleep and Chronobiology, Department of Psychiatry, and Center for Sleep and Respiratory Neurobiology University of Pennsylvania School of Medicine Philadelphia, Pennsylvania R. Key Dismukes, PhD Chief Scientist for AeroSpace Human Factors NASA Ames Research Center Moffett Field, California W. R. Ercoline, MS, PhD Manager, San Antonio Operations Life Sciences Group Wyle Laboratories San Antonio, Texas xv

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CONTRIBUTORS

Nils Erikson, MD, MPH Captain, U.S. Navy, Medical Corps Director, Aerospace Medicine Residency Naval Operational Medicine Institute Pensacola, Florida Jennifer A. Fogarty, PhD Adjunct Assistant Professor Preventive Medicine and Community Health University of Texas Medical Branch Galveston, Texas; Biomedical Risk Coordinator Space Medicine Division Johnson Space Center National Aeronautics and Space Administration Houston, Texas Namni Goel, PhD Assistant Professor Division of Sleep and Chronobiology, Department of Psychiatry, and Center for Sleep and Respiratory Neurobiology University of Pennsylvania School of Medicine Philadelphia, Pennsylvania Jerry R. Goodman, MS Manager, Acoustics Office and Lead ISS Acoustics Johnson Space Center National Aeronautics and Space Administration Houston, Texas Monica B. Gorbandt, MD Consultant, U.S. Army School of Aviation Medicine Medical Boards/Aviation Medicine Fox Army Health Center Redstone Arsenal, Alabama David P. Gradwell, PhD, MB, ChB Whittingham Professor of Aviation Medicine Faculty of Occupational Medicine Royal College of Physicians St.AndrewsPlace London, UK; Consultant Adviser in Aviation Medicine (RAF) Aviation Medicine Wing RAF Centre of Aviation Medicine Henlow, Bedfordshire, United Kingdom

Gary W. Gray, MD, PhD, FRCP (C) Consultant in Medicine Canadian Forces Environmental Medical Establishment Defence Research and Development Canada Toronto, Canada Ferdinand W. Grosveld, MS, PhD Consultant Hampton, Virginia Richard M. Harding, BSc, MBBS, PhD Principal Consultant Biodynamic Research Corporation San Antonio, Texas John D. Hastings, MD Senior Consultant in Neurology Federation Aviation Administration Tulsa, Oklahoma Steven M. Hetrick, MD, MPH Director, Occupational Medicine Program Department of Graduate Education USAF School of Aerospace Medicine San Antonio, Texas Jeffrey Hudson, PhD Biomedical Scientist for General Dynamics Wright-Patterson Air Force Base, Ohio Douglas J. Ivan, MD Chief Aerospace Ophthalmology Branch, USAF School of Aerospace Medicine Brooks Air Force Base, Texas John T. James, PhD Chief Toxicologist Habitability and Environmental Factors Division Johnson Space Center National Aeronautics and Space Administration Houston, Texas Richard T. Jennings, MD, MS Associate Professor and Director Aerospace Medicine Residency University of Texas Medical Branch Galveston, Texas

Robert Johnson, MD, MPH, MBA Associate Professor of Medicine Preventive Medicine and Community Health; The University of Texas Medical Branch Staff Physician Aviation Medical Center University of Texas Medical Branch University Hospitals Galveston, Texas David R. Jones, MD, MPH Consultant in Aerospace Psychiatry Montgomery, Alabama Robert W. Kenefick, MS, PhD, FACSM Research Physiologist Thermal and Mountain Medicine Division United States Army Research Institute of Environmental Medicine Natick, Massachusetts James A. King, MD, COL, USAF, MC, FS Chief, Emergency Medical Department Wilford Hall USAF Medical Center San Antonio, Texas Richard A. Knittig, MD, MPH Aerospace Medicine Consultant Naval Aerospace Medical Institute Pensacola, Florida William B. Kruyer, MD Chief Cardiologist Aeromedical Consultation Service USAF School of Aerospace Medicine Brooks City-Base, Texas James Perry Locke, MD, MS Flight Surgeon Flight Medicine Johnson Space Center National Aeronautics and Space Administration Houston, Texas Cheryl Lowry, MD, MPH LT COL, USAF, MC, FS Misawa Air Force Base, Japan

CONTRIBUTORS

Gregory J. Martin, MD Director, Infectious Diseases Clinical Research Program Associate Professor of Medicine & Preventive Medicine Uniformed Services University Bethesda, Maryland P. Vernon McDonald, PhD Director, Commercial Human Spaceflight Wyle Laboratories Inc. Houston, Texas Kerry McGuire University of Wisconsin Doctoral Student Johnson Space Center National Aeronautics and Space Administration Houston, Texas Glenn W. Mitchell, MD, MPH Vice-President for Clinical Safety Sisters of Mercy Health System St Louis, Missouri Stanley R. Mohler, MD, MA Professor Emeritus Aerospace Medicine Boonshoft School of Medicine Wright State University Dayton, Ohio William M. Morlang, II, DDS Associate Professor Department of Oral and Maxillofacial Pathology School of Dental Medicine Tufts University Boston, Massachusetts; Consultant in Forensic Dentistry Armed Forces Medical Examiner Armed Forces Insitute of Pathology Washington, DC David M. Musson, MD, PhD Assistant Professor Department of Anesthesia Academic Director, Center for Clinical Simulation McMaster University Hamilton, Ontario, Canada

Catherine O’Brien, MS Research Biologist Thermal and Mountain Medicine Division US Army Research Institute of Environmental Medicine Natick, Massachusetts Robert R. Orford, MD, CM, MS, MPH Assistant Professor Division of Preventive, Occupational, and Aerospace Medicine, Department of Internal Medicine Mayo Clinic Scottsdale, Arizona A. J. Parmet, MD, MPH, FACPM, FAsMA, AIAASM Instructor Viterbi School of Engineering/Aviation Safety & Security University of Southern California Los Angeles, California; Employee Health Department of Internal Medicine Saint Luke’s Hospital of Kansas City Kansas City, Missouri

xvii

Thomas Rathjen Chief, Habitability and Environmental Factors Division Johnson Space Center National Aeronautics and Space Administration Houston, Texas Eduard M. Ricaurte, MD, MS Research Physician Federal Aviation Administration Civil Aerospace Medical Institute Oklahoma City, Oklahoma Elizabeth E. Richard, MBA Strategist Wyle Laboratories, Inc. Houston, Texas Charles F. Sawin, PhD Associate Director, Space and Life Sciences Johnson Space Center National Aeronautics and Space Administration Houston, Texas

James R. Phelan, MD Assistant Clinical Professor Preventive Medicine and Community Health University of Texas Medical Branch Galveston Texas

Warren S. Silberman, DO Manager, Aeromedical Certification Division Federal Aviation Administration Civil Aeromedical Institute

Shean E. Phelps, MD, MPH, FAAFP Chief, Injury Biomechanics Branch US Army Aeromedical Research Laboratory Ort Rucker, Alabama

Suzanne D. Smith, PhD Senior Research Engineer Human Effectiveness Directorate Biosciences and Protection Division United States Air Force Wright-Patterson Air Force Base, Ohio

Jeb S. Pickard, MD, FCCP Staff Pulmonologist Aeromedical Consultation Service USAF School of Aerospace Medicine Brooks City-Base, Texas Duane L. Pierson, PhD Microbiologist Habitability and Environmental Factors Division Johnson Space Center National Aeronautics and Space Administration Houston, Texas

John A. Smyrski III, MD, MPH, MBA Lieutenant Colonel Medical Corps, Senior Flight Surgeon Aerospace Medicine and Family Medicine; Staff Physician Division Surgeon US Army: 25th Infantry Division, Schofield Barracks, Hawaii and Tripler Army Medical Center Honolulu, Hawaii

xviii

CONTRIBUTORS

Jan Stepanek, MPH, MD Assistant Professor of Medicine College of Medicine; Medical Director, Aerospace Medicine Program Divison of Preventive, Occupational and Aerospace Medicine Department of Internal Medicine Mayo Clinic Scottsdale, Arizona; Assistant Professor Preventive Medicine and Community Health The University of Texas Medical Branch Galveston, Texas James R. Strader, Jr., MD Staff Cardiologist Aeromedical Consultation Service USAF School of Aerospace Medicine Brooks City-Base, Texas Claude Thibeault, MD Clinical Associate Professor Department of Preventive and Community Health University of Texas Medical Branch Galveston, Texas Thomas J. Tredici, MD Senior Scientist Aerospace Ophthalmology Branch USAF School of Aerospace Medicine Brooks Air Force Base, Texas

Anthony P. Tvaryanas, Maj, USAF, MC, FS Chief, UAS Human Systems Integration Brooks City-Base, Texas

James M. Vanderploeg, MD, MPH Program Manager Wyle Laboratories Houston, Texas

´ Stephen J. H. Veronneau MD, MS Research Medical Officer Aerospace Medical Research Division FAA Civil Aerospace Medical Institute Oklahoma City, Oklahoma

Dougal B. Watson, MBBS, BSc Principal Medical Officer Civil Aviation Authority Petone, New Zealand

James T. Webb, MS, PhD Consultant Aerospace Physiology USAF School of Aerospace Medicine San Antonio, Texas

Mihriban Whitmore, PhD Manager, Usability Testing and Analysis Facility Johnson Space Center National Aeronautics and Space Administration Houston, Texas

Kenneth A. Williams, MD, FACEP Director, University Emergency Medicine Foundation Rhode Island Hospital Providence, Rhode Island

Kevin W. Williams, PhD Research Psychologist Human Factors Laboratory FAA Civil Aerospace Medical Institute Oklahoma City, Oklahoma

Richard S. Williams Chief Health and Medical Officer NASA Washington, DC

Gregory Zehner Senior Anthropologist, Air Force Research Laboratory Wright-Patterson Air Force Base, Ohio

CONTENTS

Foreword

iii

Foreword to 3rd Edition

v

Foreword to

2nd

Edition

vii

Foreword to

1st

Edition

ix

Preface

xi

Acknowledgments Contributors Abbreviations

xiii

xv xxiii

HISTORY CHAPTER

1

The Beginnings: Past and Present

1

J. ROBERT DILLE AND STANLEY R. MOHLER

PHYSIOLOGY AND ENVIRONMENT CHAPTER

2

Respiratory Physiology and Protection Against Hypoxia

20

JEB S. PICKARD AND DAVID P. GRADWELL

CHAPTER

3

Physiology of Decompressive Stress

46

JAN STEPANEK AND JAMES T. WEBB

CHAPTER

4

Human Response to Acceleration

83

ROBERT D. BANKS, JAMES W. BRINKLEY, RICHARD ALLNUTT, AND RICHARD M. HARDING

CHAPTER

5

Vibration and Acoustics

110

SUZANNE D. SMITH, JERRY R. GOODMAN, AND FERDINAND W. GROSVELD

CHAPTER

6

Spatial Orientation in Flight

142

A. J. PARMET AND W. R. ERCOLINE

CHAPTER

7

Thermal Stress

206

ROBERT W. KENEFICK, SAMUEL N. CHEUVRONT, JOHN W. CASTELLANI, AND CATHERINE O’BRIEN

CHAPTER

8

Cosmic Radiation

221

MICHAEL BAGSHAW AND FRANCIS A. CUCINOTTA

CHAPTER

9

Aerospace Toxicology and Microbiology

236

JOHN T. JAMES, A. J. PARMET, AND DUANE L. PIERSON

xix

xx

CONTENTS

CHAPTER

10

Space Environments

251

JAMES PERRY LOCKE

CLINICAL CHAPTER

11

Pilot Health and Aeromedical Certification

279

ROBERT R. ORFORD AND WARREN S. SILBERMAN

CHAPTER

12

Respiratory Diseases: Aeromedical Implications

306

JEB S. PICKARD AND GARY W. GRAY

CHAPTER

13

Clinical Aerospace Cardiovascular Medicine

318

JAMES R. STRADER, JR., GARY W. GRAY, AND WILLIAM B. KRUYER

CHAPTER

14

Ophthalmology in Aerospace Medicine

349

THOMAS J. TREDICI AND DOUGLAS J. IVAN

CHAPTER

15

Otolaryngology in Aerospace Medicine

380

JAMES R. PHELAN

CHAPTER

16

Aerospace Neurology

392

JOHN D. HASTINGS

CHAPTER

17

Aerospace Psychiatry

406

DAVID R. JONES

CHAPTER

18

Endocrine System and Nephrology

425

PAULA A. CORRIGAN AND CURTISS B. COOK

CHAPTER

19

Infectious Diseases

432

GLENN W. MITCHELL AND GREGORY J. MARTIN

CHAPTER

20

Dental Considerations in Aerospace Medicine

447

WILLIAM M. MORLANG, II

OPERATIONS CHAPTER

21

Occupational and Environmental Medical Support to the Aviation Industry

453

ROY L. DEHART AND STEVEN M. HETRICK

CHAPTER

22

Women’s Health Issues in Aerospace Medicine

480

MONICA B. GORBANDT AND RICHARD A. KNITTIG

CHAPTER

23

An Introduction to Human Factors in Aerospace THOMAS RATHJEN, MIHRIBAN WHITMORE, KERRY MCGUIRE, NAMNI GOEL, DAVID F. DINGES, ANTHONY P. TVARYANAS, GREGORY ZEHNER, JEFFREY HUDSON, R. KEY DISMUKES, AND DAVID M. MUSSON

491

CONTENTS

CHAPTER

24

Space Operations

xxi

516

RICHARD T. JENNINGS, CHARLES F. SAWIN, AND MICHAEL R. BARRATT

CHAPTER

25

Aircraft Accidents: Investigation and Prevention

552

´ STEPHEN J. H. VERONNEAU AND EDUARD M. RICAURTE

CHAPTER

26

Aviation Medicine in Unique Environments

624

THOMAS F. CLARKE, ROY L. DEHART, NILS ERIKSON, JAMES A. KING, CHERYL LOWRY, KENNETH A. WILLIAMS, AND ROBERT JOHNSON

CHAPTER

27

Aerospace Medicine Issues in Unique Aircraft Types

653

RICHARD S. WILLIAMS, STEPHEN L. CARPENTER, DENISE L. BAISDEN, ARNOLD A. ANGELICI, JR., STEPHEN A. BERNSTEIN, JOHN A. SMYRSKI III, DOUGAL B. WATSON, SHEAN E. PHELPS, ˜ KEVIN W. WILLIAMS, AND MELCHOR J. ANTUNANO

CHAPTER

28

The Practice of International Aerospace Medicine

683

CLAUDE THIBEAULT

THE FUTURE CHAPTER

29

Aviation, Government Space, Biomedical Innovations, and Education

694

JEFFREY R. DAVIS

CHAPTER

30

Commercial Human Space Flight ˜ MELCHOR J. ANTUNANO, JAMES M. VANDERPLOEG, RICHARD T. JENNINGS, ELIZABETH E. RICHARD, AND P. VERNON MCDONALD

Index

711

701

A B B R E V I AT I O N S

17-OHCS a A AA AA/NA AaDO2 AAMA AART AC ACAP ACC ACES ACGIH ACLS ACM AE AFB AFMIC AFRL AFSS AG AGARD AGSM AHI AL ALJ A-LOC ALPA AM AMAK AMCD AMDA AME AMIP AMP ANDES ANPRM ANR ANSI AOPA APA API APS APU

17-hydroxy corticosteroid acceleration anterior aeronautical adaptability Alcoholics/Narcotics Anonymous alveolar/arterial oxygen difference Army Aeromedical Activity Aircraft Accident Research Team aberrant conduction Aeromedical Consultants Advisory Panel Air Combat Command (formerly TAC) advanced concept ejection seat or advanced crew escape suit American Conference of Governmental Industrial Hygienists advanced cardiac life support aerial combat maneuver aeromedical evacuation Air Force Base Armed Forces Medical Intelligence Center Air Force Research Laboratory automated flight service stations artificial gravity Advisory Group for Aerospace Research and Development anti-g straining maneuver apnea-hypoxia index arbitrary limit Administrative Law Judge almost loss of consciousness Airline Pilots Association Aerospace Medicine airway medical accessory kit Aeromedical Certification Division Airline Medical Directors Association aviation medical examiner Aircraft Mishap Investigation and Prevention Aerospace Medical Professional Aircraft Noise Design Effects Study advanced notice of proposed rule making active noise reduction American National Standards Institute Aircraft Owner’s and Pilot’s Association Aviation Medical Physician Assistants Aviation Preflight Indoctrination accident prevention specialist auxiliary power unit

AR AR ARMA ARTCC AS ASHRAE

ASI ASR ATA ATAGS ATCS ATCT ATLS ATM ATP AV BAD BAV BEI BNC bpm BPT BTPS BV BW C C3 CABG CAD CAF CAMI CCAT CCK CERAP CFC CFIT CG CHeCS CLL CMO CMS CNS CO CO

aortic regurgitation advisory report Adaptability Rating for Military Aeronautics Air Route Traffic Control Centers aortic stenosis American Society of Heating, Refrigerating, and Air Conditioning Engineers Italian Space Agency automatic speech recognition atmospheres absolute advanced technology anti-G suite air traffic control specialists air traffic control towers advanced trauma life support air traffic management air transport pilot atrioventricular bipolar affective disorder bicuspid aortic valve biological exposure indices balanced noise criteria beats per minute bronchial provocation test body temperature, pressure saturated blood volume bacteriological warfare cervical vertebra Command, Control and Communications coronary artery bypass graft coronary artery disease coronary artery fluoroscopy Civil Aeromedical Institute Critical Core Air Transport contaminant clean-up kit combined enroute and approach center chlorofluorocarbons controlled flight into terrain center of gravity Crew Health Care System central light loss crew medical officer countermeasures system central nervous system cardiac output carbon monoxide

xxiii

xxiv

A B B R E V I AT I O N S

CO2 COPD CPAP CPAP CPK CRM CRV CSA CSD CSF CT CTT CTV CVP CW d DAET DAI DARA dB DCIEM DCS DEXA DLCO DLW DMORT DNBI DO DoD DOT DRT DS DSM IV DLR E EBCT ECG ECLSS ECT EDO EEG EFIS EHS EMK EMU ENEV(Canada) EOG

carbon dioxide chronic obstructive pulmonary disease continuous positive airway pressure continuous positive pressure assisted breathing creatine phosphokinase crew resource management crew return vehicle Canadian Space Agency cortical spreading depression cerebral spinal fluid computed tomography color threshold test crew transport vehicle central venous pressure chemical warfare specific density of blood Department of Aviation Medicine Education and Training diffuse axonal injury Deutsche Agentur fur Raumfahrtangelenheiten decibel Canadian Defense and Civil Institute of Environmental Medicine decompression sickness dual energy x-ray absorptiometry diffusing capacity, carbon monoxide doubly labeled water Disaster Mortuary Operational Response Team disease and/or non-battle injury dissolved oxygen Department of Defense Department of Transportation Diagnostic Rhyme Test dead space, lung Diagnostic and Statistical Manual of Mental Disorder, Fourth edition Germany’s Aerospace Research Center and Space Agency epinephrine electron beam computed tomography electrocardiogram or graph environmental control and life support system equivalent chill temperature extended duration orbiter electroencephalogram or graph electronic flight information systems environmental health system emergency medical kit extravehicular maneuvering unit or extravehicular mobility unit estimated no effects value electrooculography

EPT ERV ESA ESP ET EVA F FAA FAR FDPB FEF50 FEV1 FFS FFT FLIR FM FoF FRC FS FSDO g G GCR GE GERD GHz G-LOC GMO GOR GPS GWP +Gx +Gz ±Gy −Gx −Gz h +H HALO HBO HCM HEEDS HEMA HEPA HFACS HGP HIMS HMD HMO HMS HR HSG HSP HTG HUT Hz

effective performance time expiratory reserve volume European Space Agency erholungspulssume (sum of heart beats) effective temperature extravehicular activity force Federal Aviation Administration Federal Aviation Regulations fatigue–decreased proficiency boundary forced expiratory flow at 50% forced expiratory volume at 1 second Frank’s flying anti-G suit fast Fourier transformation forward looking infrared frequency modulation fear of flying functional reserve capacity flight surgeon(s) Flight Service District Office gravitational constant of 9.81 m/sec2 acceleration-induced inertial force galactic cosmic radiation gastric emptying gastroesophageal reflux disorder giga Hertz G-induced loss of consciousness General Medical Officer gradual onset rate global positioning system global warming potential positive transverse G (A to P) positive vertical G positive/negative lateral (side to side) negative transverse G (P to A) negative vertical G blood column height (mm) hydrogen ion high-altitude, low-opening hyperbaric medicine hypertropic cardiomyopathy helicopter emergency egress device hydroxyethylmethacrylate High-efficiency particulate air Human Factors Analysis and Classification System hard gas permeable (lenses) Human Intervention Motivation Survey helmet mounted display health maintenance organization health maintenance system heart rate (beats per minute) high sustained G health stabilization program high-G tolerance group head-up tilt table Hertz

A B B R E V I AT I O N S

I IAM IATA IC ICAO IEEE IGF-I IHR ILD IMS INR IP IRB ISO ISS IVCD JAA JSC K km kPa KSC KW L-1 LAD LAHB LAMPS LASIK LBBB LBNP LCG LDH LEO LEP LEQ LES LiOH LOC LOS LSAH LTG LVH m m/s m/s2 M-1 MAK MBK MCC MCCH MCV MEDEVAC MEDOP MEF MFB mg

inspired Institute of Aviation Medicine International Air Transport Association inspiratory capacity International Civil Aviation Organization Institute of Electrical and Electronics Engineers Insulin-like growth factor I International Health Regulations interstitial lung disease Integrated Medical System international normalized ratios International Partners Institutional Review Board International Standards Organization International Space Station intraventricular conduction delay (Europe) Joint Aviation Authorities Johnson Space Center constant of 1 G tolerance increase kilometer kilopascal Kennedy Space Center kilowatt type of AGSM left axis deviation left anterior hemiblock light airborne multipurpose system laser in-situ keratomileusis left bundle branch block lower body negative pressure liquid cooling garment lactate dehydrogenase low earth orbit laser eye protection equivalent continuous noise launch and entry suits lithium hydroxide loss of consciousness line of sight Longitudinal Study of Astronaut Health low-G tolerance group left ventricular hypertrophy mass or meter velocity: meters/second acceleration: meters/second2 Maneuver number 1; a type of AGSM medical accessory kit medication and bandage kit Mission Control Center Mission Control Center Houston mean corpuscular volume aeromedical evacuation Medical Extended Duration Orbiter Pack Marine Expeditionary Force Multifunctional Battalions milligrams

MHz MI MMFR mm Hg MMIS MOOTW MPH MPSR MR MRI MRT MS MS MSE MSLT MVP MW MWT NAA NAIMS NAMI NAMRL NAS NAS NASA NASDA NATO NAWC NBC NC NCRP NE NIR No. 14CFR NORAD NOx NPRM NRR NSAID NTSB NVG O2 OBS OOM OSA OSAPL OSHA OTC P Pa Pa PA

xxv

MegaHertz myocardial infarction mid-maximal expiratory flow rate mm mercury Military Man-In-Space military operations other than war Master of Public Health multipurpose support room mitral regurgitation magnetic resonance imaging modified rhyme test mitral stenosis multiple sclerosis mental status evaluation multiple sleep latency testing mitral valve prolapse milliwatt maintenance of wakefulness testing not aeronautically adaptable National Airspace System Information Monitoring System Naval Aerospace Medical Institute Naval Aeromedical Research Laboratory Naval Air Station National Airspace System National Aeronautics and Space Administration National Space Development Agency of Japan North Atlantic Treaty Organization Naval Air Warfare Center Nuclear, Biological and Chemical noise criteria National Council on Radiation Protection norepinephrine nonionizing radiation Title 14 of the Code of Federal Regulations North American Air Defense Command oxides of nitrogen Notice of Proposed Rule Making noise reduction rating nonsteroidal anti-inflammatory drug National Transportation Safety Board night vision goggles oxygen operational bioinstrumentation system on-orbit maintenance task allocation obstructive sleep apnea overall sound pressure level Occupational Safety and Health Administration over-the-counter posterior or pressure Pascal arterial blood pressure (mm Hg) pulmonary alveolar pressure

xxvi

PAC PACO2 PAO2 PAO2 PB PBG PCM PDAY PEFR PET PFT PH PLL PMC PMMA PMR PN PO2 PP PPB PPG PRK PSD PSG PSI psi psig PSP PTA PTCA PTS PTSD PVC Q RAD RAF RAM RBBB RBC RBCM RCB REM RF RFS RK ROR RQ RSA RSC RSS RTFS RTLS RV SNR

A B B R E V I AT I O N S

premature atrial contraction arteria0l CO2 partial pressure alveolar oxygen tension arterial oxygen partial pressure phonetically balanced positive pressure breathing during G exposure primary care manager pathobiological determinants of atherosclerosis of youth peak expiratory flow rate positron emission tomography pulmonary function test hydrostatic pressure (mm Hg) peripheral light loss private medical conference polymethyline-thacrylate proportionate mortality ratio perceived noisiness oxygen partial pressure partial pressure positive pressure breathing positive pressure ‘‘g’’ protection photorefractive keratectomy power spectral density polysomnography pounds per square inch pounds of pressure per square inch pounds of pressure per square inch - gas primary spontaneous pneumothorax posttraumatic amnesia percutaneous transluminal angioplasty permanent threshold shift posttraumatic stress disorder premature ventricular contraction blood perfusion rate right axis deviation Royal Air Force Residency in Aerospace Medicine right bundle branch block red blood cell red blood cell mass reduced comfort boundary rapid eye movement radio frequency Regional Flight Surgeon radial keratotomy rapid onset rate respiratory quotient Russian Space Agency Russian System of Countermeasures recumbent seating system returned to flying status return-to-launch site residual volume signal to noise ratio

Sa SACM SEE SGOT SII SIL SLT SMAC SMO SMR SMS SODA SOMS SOs SPE(s) SR SSRI STI STPD STS SVOC TAC TAL TBI TCCS TCD TCP TEE TGA TLC TLV TLV TRACON TTS TUC TV TWA UAV UK URLs USAAF USAF USAFSAM USASAM USN V ˙ Q ˙ V/ VC VHMs VOC VOR VR

arterial oxygen saturation simulated aerial combat maneuver shuttle emergency eyewash kit serum glutamic-oxaloacetic transaminase speech intelligibility index speech interference levels signal light test space maximum allowable concentration Senior Medical Officer standardized mortality rate space motion sickness Statement of Demonstrated Ability shuttle orbiter medical systems oxides of sulfa solar particle events sweat rate serotonin specific uptake inhibitors speech transmission index standard temperature, pressure, dry significant threshold shift or Space Transportation System semi-volatile organic compound(s) Tactical Air Command transoceanic abort landing traumatic brain injury trace contaminant control system transcranial Doppler tri-cresyl phosphate total energy expenditure transient global amnesia total lung capacity threshold limit value total lung volume terminal radar control center temporary threshold shift time of useful consciousness tidal volume time weighted average unrestricted aerial vehicles United Kingdom universal resource locators United States Army Air Force United States Air Force United States Air Force School of Aerospace Medicine United States Army School of Aviation Medicine United States Navy pulmonary ventilation rate ventilation–perfusion ratio vital capacity voluntary head movements volatile organic compound(s) vestibulo-ocular reflex venous return

A B B R E V I AT I O N S

VT VTG VTOL W w

ventricular tachycardia volume thoracic gas vertical take off and landing watt weight

WBGT WCS WHO WPW WWII

wet bulb globe temperature (shuttle) waste collection system World Health Organization Wolff-Parkinson-White syndrome World War II

xxvii

CHAPTER

1

The Beginnings: Past and Present J. Robert Dille and Stanley R. Mohler

Thus do men serve history and history the ages. —Eddie Rickenbacker

History started today, not only yesterday. —Anon.

EARLIEST CONCEPTUALIZATIONS As prehistoric people made grueling trips across trackless lands, they surely must have envied the swift, graceful, and seemingly effortless flight of birds. Fantasies and legends involving wings and flight by gods, angels, rulers, and guardians occur in the folklore of nearly every culture. Windmills, kites, parachutes, and the rocket (the latter from China where gunpowder was invented about 900 AD) were early inventions bearing upon the pursuit of human flight. The legend of father and son, Daedalus and Icarus, states that they made wings of feathers held together by wax to escape from King Minos’ Crete. During escape, Icarus ignored Daedalus’ admonishments, and flew too near the sun: the wax melted and he fell into the sea. Roger Bacon, a 13th century Franciscan monk, was quoted as hearing about artificial wings that turned about a sitting person and beat the air ‘‘after the manner of a flying bird.’’ Leonardo da Vinci designed a parachute in 1500. He also drew pictures of hypothetical human-powered helicopter and ornithopter flying machines. Leonardo died in 1519 AD, and his approximately 500 pages of notes and 1,500 sketches were forgotten for more than 300 years. If available earlier, these writings could possibly have accelerated the course of aeronautical development. Many legends, figures, and fantasies attest to our early predecessors’ fascination with the possibilities of human flight, an achievement that awaited the coalescence of

intuition, technologic advances, and goal-driven experimentation. Of course, human tolerances to higher altitudes and in-flight acceleration forces awaited actual flight experiences before awareness of these aspects arose. In addition, the need for occupant restraint systems, crashworthiness protection, and a means to deal with in-flight spatial disorientation under conditions of loss of outside visual reference, also awaited flight experience. The general sequence of topics in this chapter proceeds from the earliest conceptualizations by century, flowing through the 16th century. This latter European ‘‘Age of Reason’’ launched the 17th century ‘‘Age of Enlightenment.’’ Topics to be covered include the aeromedical implications of the first ‘‘mountain sickness’’ reports along with early laboratory gas studies and the hypoxic experiences of balloonists. The December 17, 1903 first flight of a heavier-than-air powered aircraft piloted by the Wright Brothers launched the basis for an explosive growth of aviation and the need for medical support of aviators. The April 12, 1961 earthorbiting flight of Yuri Gagarin, of the Union of Soviet Socialist Republics (USSR), opened the era of human space flight. The chapter concludes citing the development of space medicine, bringing us to the July 20, 1969 Apollo 11 moon landing by the National Aeronautics and Space Administration (NASA). The moon landing was conducted by Neil Armstrong and Edwin Aldrin Jr., the first two humans to walk on a heavenly body other than the earth, while Michael Collins, their orbiting Command Module Pilot circled overhead. 1

2

HISTORY

SIXTEENTH CENTURY EXPERIENCES Discomfort with mountain travel was documented after the Spanish army under Cortez attacked Mexico in 1519. In addition, the Spanish army under Pizarro experienced mountain sickness 25 years later while conquering areas subsequently known as Ecuador, Chile, and Peru. Later in the century, Jesuit Father Jose de Acosta blamed the air of lofty places. On five crossings over the Andes, he noted a loss of appetite, the presence of nausea and abdominal pain, in addition to vomiting of food, phlegm, bile, and blood. Father Acosta had profound weakness and had to be supported on his horse; he also had dizziness and was panting. Upon return to lower altitude, the symptoms shortly disappeared. Acosta wrote ‘‘Not only men feel this, animals do too, and sometimes stop so that no spur can make them advance.’’ Acosta was ‘‘convinced that the element of the air is in this place so thin and so delicate that it is not proportioned to human breathing which requires it denser and more temperate.’’ Acosta’s account was published in Seville in 1590 but is best found in the Hitchcock (1) translation of Bert’s Barometric Pressure. The book, originally published in French in 1878, contains 264 references on mountain sickness. Scientific studies on the effects, prevention, and treatment of acute and chronic mountain (altitude) sickness, pulmonary edema, and cerebral edema have been conducted in the Andes, on Mt. McKinley, and in the Himalayas. Scientists who conducted this research included McFarland, Hurtado, Hultgren, and Krakauer.

SEVENTEENTH AND EIGHTEENTH CENTURY PROGRESS Evangelista Torricelli (1608–1647), an Italian physicist, invented the mercury barometer 50 years after Acosta’s observations. He studied the response of small animals to vacuum. Otto von Guericke (1602–1686), engineer, of Germany, invented the pneumatic pump in 1672. He studied how candle flames were extinguished, animals could not live, and sounds would not travel under vacuum. He also showed that horses could not pull apart two vacuumcontaining hemispheres. Robert Boyle (1627–1691), Irish natural philosopher, observed bubbles in the eye of a viper following its decompression in a vacuum environment. He discovered that at a constant temperature the volume of gas varies inversely with pressure—the famous ‘‘Boyle’s Law.’’ Joseph Priestly (1733–1804), English scientist, and Antoine Lavoisier (1743–1794), French chemist, are separately credited with discovering oxygen. During 1783, brothers Joseph and Etienne Montgolfier of France successfully launched hot air balloons, using burning damp straw, wool, and occasionally old shoes and even old meat in the mix. A rooster, a duck, and a sheep were hefted by hot air on September 19 of that year. On October 15, the brothers lifted Pilatre de Rozier, an apothecary of Metz, in a

tethered hot air balloon to a height of 50 ft. On November 23, de Rozier and Francois Laurent Marquis d’Arlandes were free floated across Paris in a hot air balloon. American ambassador to France, Benjamin Franklin, observed that these developments in ballooning foretold a promising future. Professor Jacques Alexandre Cesar Charles (1746–1823), along with Joseph Louis Gay-Lussac (1778–1850), articulated what is now known as Charles’ Law that states ‘‘At a constant pressure, a given amount of gas will expand its volume in direct proportion to the absolute temperature.’’ Charles invented the hydrogen balloon in 1783 and made a flight on December 1 with a companion (the balloon’s maker). After the companion left the balloon after a 1-hour 45-minute flight, the lightened balloon immediately rose to an altitude of 3,048 m (10,000 ft). Charles reported right ear and maxillary pain with increasing altitude, and this report is usually considered the first case of aerotitis. Early in the next century, Gay-Lussac made a balloon flight, on September 16, 1804, to an altitude of over 7,016 m (23,000 ft), a record that stood for approximately a half century. Trained in Scotland and loyal to King George III, Boston physician John Jeffries moved to London at the beginning of the Revolutionary War. He, along with crowds estimated at 150,000 to 250,000, gathered to observe balloon ascents by John Pierre Blanchard and the Italian, Vincent Lunardi. Jeffries paid Blanchard 100 guineas to fly from London to Kent in a hydrogen balloon. On the flight, Jeffries carried a thermometer, barometer, pocket electrometer, hydrometer, precision timepiece, compass, small telescope, and seven sealed vials to collect air samples at different altitudes for Henry Cavendish, the discoverer of hydrogen. The results were reported to the Royal Society. Blanchard had announced his intention to fly across the English Channel before agreeing to take Jeffries along. Again, Jeffries agreed to pay the expenses of the flight, and, if necessary to save Blanchard, he would jump into the channel. Blanchard, in a bit of deviousness, ordered a vest lined with lead to keep the balloon from lifting, forcing Jeffries out. The tailor mistakenly sent the vest to Dr. Jeffries at a hotel in Dover, and the ruse was uncovered. On January 7, 1785, the two were the first to cross the English Channel, and Jeffries became the first paying aerial passenger on an international flight. They carried the first over-water survival gear, cork vests, and equipment required during the over-water flight. Jeffries reported visual illusions: ‘‘we were fixed and objects appeared to pass to or from us or revolve around us.’’ He also reported that ‘‘we were enveloped by a certain stillness that could be felt’’ (possibly sensory deprivation). At one point it was almost necessary for Jeffries to jump into the water. Later, close to a hard landing, most of their clothing, the celebration bottle of brandy, the life vests, and all equipment except the barometer, were jettisoned. To soften the landing in France, Jeffries thought to eliminate ‘‘five to six pounds of urine.’’ A letter from Benjamin Franklin’s son in London, to his son who was with his grandfather in Paris was delivered, the first airmailed letter.

CHAPTER 1

Jeffries’ accounts have been reprinted in Aviation, Space, and Environmental Medicine (2,3). In 1789, Dr. Jeffries returned to Boston and practiced medicine until his death in 1819. He was active in teaching, and gave the first public lecture on anatomy. He was a founder of the Boston Medical Library. Jeffries helped Blanchard to make the first hydrogen balloon free flight in America on January 9, 1793. This event occurred in Philadelphia with the departure from the yard of the Walnut Street prison. A large crowd observed the departing flight, including President George Washington and the French Ambassador. Washington gave Blanchard a letter of introduction (Blanchard’s English was not very good, hence the letter for those he may meet on landing—some consider this the first U.S. passport). Blanchard’s pulse rate data collected for Dr. Benjamin Rush was 84 beats/minute on the ground and 92 at 1,772 m (5,812 ft). Six air samples were collected for Dr. Casper Wistar. The balloon landed in Gloucester County, New Jersey. Blanchard returned to Europe and made a number of flights in various countries. While flying over The Hague, Netherlands, he is reported to have had an in-flight heart attack, falling more than 50 ft. He died on March 7, 1809, the first pilot in command to have an in-flight incapacitating cardiac event. On June 15, 1785, Pilatre de Rozier, the first person lifted by the Montgolfiers, accompanied by a companion, Pierre Romain, attempted to cross the channel from France to Britain in a combination hydrogen–hot air balloon. The hydrogen caught fire half an hour after take-off and both died in the accident, the first aeronautic fatalities. De Rozier’s fianc´ee, Susan Dyer, witnessed the explosion, collapsed, and died.

THE NINETEENTH CENTURY A Belgian physicist, Etienne Robertson, ascended to approximately 7,000 m (22,966 ft) with a music teacher named Lhoest, at Hamburg, Germany, on July 18, 1803. He described a hurried pulse, mental and physical apathy, and an indifference instead of his usual glory and passion for discoveries. He reported that his lips had swelled from blood rushing there and his hat seemed too small. He was able to place his hand in boiling water without feeling pain. He flew with Russia’s first aeronaut, Sacharoff, on June 30, 1804. Robertson’s son, Eugene, ascended to 6,000 m (21,000 ft) at Castle Garden, New York, on October 16, 1826. Dr. Claude Bernard (1813–1878) of France is considered the founder of experimental medicine. He studied the effects of illness, carbon dioxide, cold, and superoxygenated air on hypoxia tolerance. He studied carbon monoxide combination with hemoglobin as a cause of oxygen starvation. While studying the liver, he discovered that liver glycogen (he gave the substance its name) broke down to glucose, elucidating the glucose–glycogen relationship. Paul Bert (1833–1886), considered by some to be the father of aviation medicine, was born in Auxerre, Yonne,

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France. He was trained in engineering, law, physiology, and medicine. He succeeded his mentor, Claude Bernard, to the chair of physiology, Faculte’ des Sciences, Paris. He conducted extensive work in the early 1870s, the latter culminating in his classic book, La Pression Barom´etrique, Recherches de Physiologie Exp´erimentale in 1878. Mary Alice and Fred Hitchcock translated the volume into English during World War II. Bert undertook studies to explain the symptoms reported by aeronauts during their balloon ascensions. He conducted 670 experiments in bell jars and an altitude chamber of his construction. He used plants, sparrows, rabbits, guinea pigs, cats, dogs, and humans, and reported the findings in his book. He established that death occurred at a partial pressure of oxygen of 35 mm Hg, irrespective of atmospheric pressure. He found that the intermittent inhalation of air rich in oxygen relieved symptoms of hypoxia. He also recognized that excess carbonic acid in the blood and tissues created adverse effects. The hazard of loss of too much carbon dioxide through hyperventilation was apparently not recognized. Bert died as Resident General, Tonkin province, French Indochina, at age 53, on November 11, 1886, during an attack of dysentery. James Glaisher (1809–1903) and his balloon engineer, Henry Coxwell (1819–1900), made several ascents to high altitudes over England to relatively high altitudes without supplemental oxygen. On September 5, 1862, reaching 8,839 m (29,000 ft), Glaisher was unconscious for an estimated 7 minutes. It is reported that the two balloonists experienced some acclimatization to high altitudes without turning blue or having difficulty breathing. Henri Sivel, a naval officer, and Joseph Croce-Spinelli, a journalist, ascended on March 22, 1874, in the balloon, Polar Star, to a height of 7,300 m (23, 950 ft). They carried bags provided by Bert containing 40% and 70% oxygen, the former to be breathed on reachi ng 3,600 m (11,811 ft) and the latter on reaching 6,000 m (19,685 ft). It was observed that the oxygen improved strength, alertness, memory, visual acuity, and appetite. On April 15, 1875, they, along with a third aeronaut, Gaston Tissandier, launched in the balloon, Zenith, with goldbeater’s bags (made from the cecum of an ox) of 65% and 70% oxygen. They sought to reach an altitude well above 8,000 m (26,246 ft), exceeding Glaisher’s and Coxwell’s September 5, 1862 record. Bert sent a message that the French balloonists did not have sufficient oxygen, but they had lifted off before the arrival of the message. At 7,450 m (24, 442 ft) they cut three bags of ballast, probably in a state of hypoxic euphoria, and climbed to an estimated 8,600 m (28, 215 ft). All three lost consciousness and Sivel and CroceSpinelli died in-flight. Tissandier passed out, coming to some time later as the balloon had spontaneously descended to a lower altitude and struck the ground. In the third edition of his Principles and Practice of Aviation Medicine (4), Armstrong wrote, ‘‘the first use of air transportation in support of medical activities occurred during the Siege of Paris in 1870 when a total of 160 patients were removed from the city by means of an observation

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balloon.’’ Lam has examined the records and found that no passengers were patients (5). The records contain the names of the balloonists, the weights of the mail, and the landing sites. The flights occurred between September 23, 1870 and January 21, 1871, during the Paris siege as the Franco-Prussian war continued. Tissandier was one of the balloonists but most were sailors.

TWENTIETH CENTURY: EXPONENTIAL GROWTH OF AEROSPACE MEDICINE The invention of the practical heavier-than-air powered and controlled flight by Wilbur and Orville Wright of Dayton, Ohio, initially proved by them on December 17, 1903 at Kitty Hawk, North Carolina, was followed in the years before World War I by flight schools and derivative aircraft in all parts of the world. Large dirigibles also evolved, and the German Naval Airship Division conducted air raids over London, flying at 5,000 to 6,000 m (16,400–20,000 ft) whenever possible to avoid airplane attacks. Eight hours of cold, hypoxia, and engine noise caused documented dizziness, tinnitus, headache, increased heart and respiration rates, and fatigue. The supplied compressed oxygen had an unpleasant oily taste. Crewmembers and commanders were reluctant to use oxygen, despite symptoms, because to do so was considered as a sign of weakness. Liquid oxygen was later used because more could be carried, weight for weight, than as a gas (4). On February 7, 1912, the U.S. War Department published instructions concerning the physical examination for candidates with respect to aviation duties. These instructions were preceded by the 1910 minimum medical standards for military pilots that were developed in Germany, the first country to establish such standards. Soon afterward, the Italian Air Medical Service followed suit. The French and British established military pilot medical standards in 1912. The U.S. military established detailed physical standards for aviators under the guidance of Theodore C. Lyster in 1916. These were published in 1919 as the Air Service Medical (6). With respect to the early standards, the British emphasized cardiovascular performance and hypoxia tolerance with a rebreather bag that progressively decreased the oxygen to simulate the decrease in oxygen pressure at higher altitudes. The French added vestibular function and neurovascular steadiness in the presence of an unexpected gunshot. The Italians emphasized reaction time. When the United States acquired its first airplane in 1908, the general army duty medical standards applied. These emphasized the dental characteristics, a holdover from the Civil War era when enlisted men needed to be able to pull a cork by the teeth from a powder flask. The 1912 draft aviation medical standards emphasized normal vision, normal hearing and eardrums, and the visual ability to determine distances. Disqualification included colorblindness, acute or chronic disease of the middle or inner ear, or auditory nerve, or any disease of the respiratory, circulatory, or nervous system. Equilibrium was

tested by standing with the eyes closed, and then hopping with the eyes open and then closed. In 1914 new arbitrary, more rigorous standards, were ordered by the Surgeon General, but failure rates were so high for new young applicant officers that the standards were relaxed. One screening test involved the candidate holding a needle between the thumb and forefinger. A blank pistol was fired behind the candidate’s head. If the startle reaction produced blood, the candidate was disqualified. During the first year of flying in World War I, when there was little combat, the English and French found that 2% of aircraft accidents were due to combat, 8% were due to mechanical problems, and 90% were due to human failure; two thirds of these 90% were reported to be due to physical defects (6). The U.S. medical personnel thought that a considerable proportion of the physical defects leading to accidents ‘‘are the immediate or late effects of strain on the circulation under the influence of low oxygen tension in the air’’ (6). Some soldiers disqualified for further combat because of battle fatigue, shell shock, and neurocirculatory asthenia became pilots. The Royal Air Force (RAF) of the United Kingdom started a Care of Flyer Service. This activity reduced pilot deficiency accidents over 2 years from 60% to 12%. Improved physical standards, examinations, flight training, and attention to physical and emotional problems undoubtedly contributed to this decline. Even so, many aces had physical defects that would be disqualifying by current standards. Roy Brown, who shot down top ace Baron Manfred von Richthofen (80 victories) in 1918, had chronic stomach distress, requiring the regular consumption of soda, milk, and brandy. American pilot Elliott Springs (5 victories) consumed milk of magnesia and gin, alternately, to relieve chronic stomach symptoms. ‘‘Eddie’’ Rickenbacker (26 victories) required a mastoidectomy during the war. French ‘‘ace of aces,’’ Georges Guynemer (53 victories) disappeared during a flight that was preceded by emotional strain and a crash-induced concussion and knee injury. A little-known pilot with the name of Veil, when asked why he stayed with the Lafayette Flying Corps when the United States came into the war, stated that he would not qualify in the U.S. air arm because he had ‘‘a game leg, a stiff neck, a hole in my groin, and a blood disease among other things.’’ Britain’s top ace, 34-year-old Mike Mannock (73 victories) was nearly blind in the left eye from a congenital condition. American William Thaw (5 victories), Lafayette Escadrille and later U.S. 103rd Aero Squadron, had normal vision in only one eye. Lt. Frank Alberry of Australia lost his right leg in ground combat in 1916. He was determined to fly as he could not be a ground troop with an artificial leg. He sought an audience with the King, and obtained a letter of acceptance. He took this to the Air Board, went through pilot training, and shot down seven enemy aircraft. In 1921, the New Australian Air Force would not accept him for flight service.

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German ace Oswald Boelcke (40 victories), had severe asthmatic attacks and Georg Zeumer, skilled pilot and 1915 combat instructor of Baron von Richthofen, was a ‘‘lunger’’ with advanced tuberculosis, chronic coughing, and a very unhealthy appearance. Flying was considered a seated sedentary activity, a factor in the decisions to allow certain soldiers too impaired to be in the trenches to take to the air. The U.S. Army had issued orders forbidding hard landings and the wearing of spurs in the cockpit. In May 1917, the Army established new medical standards for flight crew, including normal eye muscle balance, fusion, intraocular tension, visual field, near-vision accommodation, and the ability to clear the ears on descent. A turning chair test took the place of the stand, walk, and hop test. Specially trained physicians at 35 centers in the United States conducted the examinations. Theodore C. Lyster, MD, Chief Surgeon of the U.S. Army Aviation Section, selected in May 1917 Isaac H. Jones, MD, a Philadelphia otologist, to open the first of the 35 medical examination centers at the University of Pennsylvania Hospital. In December, Dr. Lyster and Dr. Jones spent 3 months in Europe, assessing the medical problems facing aviators. On return, they established the Air Service Medical Research Laboratory at Hazelhurst Field, Mineola, Long Island, New York. William H. Wilmer, MD was put in charge. This new facility contained a low-pressure chamber, allowing the program to conduct pioneering studies in aviation physiology aspects and aircrew protection from hypoxia. The above-mentioned principals established a medical research board on October 18, 1917 to investigate conditions that affect the efficiency of pilots, to carry out tests on pilot abilities to fly at high altitudes, to carry out tests on suitable equipment to supply oxygen to pilots, and to act as a standing medical board on matters relating to the physical fitness of pilots. Examination procedures and research at the laboratory are provided in Air Service Medical (6). A program at the new laboratory instituted selection and training measures for new aeromedical examiners. Isaac Jones, MD, and fellow otologist, Eugene R. Lewis, MD, recommended that the examiners fly regularly. Lewis introduced the new term for these physicians, flight surgeons. Pilots and commanding officers were to be counseled with respect to an airman’s condition that warranted temporary or permanent ‘‘grounding.’’ The first flight surgeon to report for active duty at a U.S. base was Capt. Robert J. Hunter. From Park Field, Tennessee, Dr. Hunter submitted a report dated May 13, 1918 to Dr. Lyster documenting early efforts to reduce accidents. The report stated that 63 candidates were interviewed, a sick call was held on May 27, a rest period was established between 11:00 AM and 3:00 PM, and athletic and recreation exercises were to be held twice/week. Sanitary cups in the field and shady areas for cadets were instituted. Three nonfatal accidents were investigated, one due to inexperience, one possibly due to hitting the head on the cowl during a loop, and one due to chasing a crow. Discussions with the mess

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officer were undertaken. Hunter acted as a member of a special board in several cases to consider whether further instruction of certain cadets should be continued. Dr. Isaac Jones believed that the doctor who flies best understands the pilot. He taught that keeping pilots mentally and physically fit to continue flying was the main purpose of flight surgeons. He reportedly said that it might take 100 years to convince pilots not to feel that the main purpose of flight surgeons is to find a way to not let pilots fly. Jones and Lewis probably coauthored Air Service Medical and Jones also wrote Equilibrium and Vertigo, 1918. Raymond E. Longacre, MD, a 1921 graduate of the new flight surgeon school, developed for the first time a set of personality criteria for selecting candidates for flight training. Following World War I, Hazelhurst Field was converted to a private airport (Roosevelt Field), and the medical research facility was moved in 1919 to nearby Mitchel Field. In 1926 the facility again moved, this time to Brooks Field, San Antonio. Later it moved to Randolph Field and subsequently back to Brooks. In 1924, the National Geographic Magazine stated, ‘‘Perhaps the most heroic test of an aviator’s grit and stamina is an altitude climb’’ (7). Rudolph W. ‘‘Shorty’’ Schroeder of McCook Field, Dayton, Ohio, began to set altitude records in 1918, reaching 10,093 m (33,114 ft) on February 27, 1920, his third record. He used a LePere LUSAC-11 (LePere U.S. Army Combat) open cockpit American-produced two-seat biplane that resembled the British Bristol fighter. It had a GE Moss supercharger powered by exhaust gases to boost air to its 400 hp Liberty engine. Schroeder’s oxygen gave out at the peak altitude and he lost consciousness. He recovered at 914.4 m (3,000 ft) after losing 9,144 m (30,000 ft) in 2 minutes and landed at the edge of the river near McCook Field. There were other problems, including ice in the oxygen tubes and carbon monoxide. The flight was a major demonstration of capabilities and deficiencies in pursuing high-altitude flights. John A. Macready followed the Schroeder flights in the same aircraft and reached 11,521 m (37,800 ft) on September 28, 1921. He wore suits of woolen underwear, his regulation uniform, a knitted wool garment, a leather suit padded with down and feathers, fur-lined gloves, fleece-lined moccasins over the boots, and goggles treated with an antifreeze gelatin (Figure 1-1). An oxygen tube was attached to a pipestem mouthpiece. A mask protected the face from freezing at the −67◦ F range of air temperature. Macready and Oakley Kelly made the first nonstop transcontinental airplane flight in a Fokker T-2 monoplane across the United States, departing Roosevelt Field, Long Island, New York, at 12:36 PM (EST) on May 2, 1923, and landing at Rockwell Field, San Diego, California, at 3:26 PM (EST) on May 3, a flight of 26 hours and 50 minutes covering 2,516 mi. The pilots had made two prior ‘‘endurance’’ cross-country flights in the Fokker to test their physical capabilities on such long flights as well as the aircraft and its equipment. The pilot in the open cockpit just behind the engine could check the maps en route while the other pilot in the fuselage with side windows kept the wings level with a set of controls, a ‘‘human autopilot.’’ Kelly made

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FIGURE 1-1 Lt. John A. Macready, U.S. Army Engineering Division test pilot, McCook Field, Ohio, dressed for his record ascent to 11,521 m (37,800 ft) on September 28, 1921.

the take-off from Roosevelt Field and Macready made the landing at Rockwell Field. The pilot seat back was modified so that the two could change places periodically during the long flight. Macready made the first night parachute jump when engine failure occurred at 518 m (1,700 ft) on June 18, 1924. He landed unhurt. He also set National Aeronautic Association altitude and duration records in a bomber in 1924, and reached 11,796 m (38,700 ft) in an XCO5 aircraft with a turbosupercharger on January 29, 1926. Some scientists in 1923 reportedly told Macready that he might cross a boundary beyond the pull of gravity and become a space satellite. Lt. Harold R. Harris, Flying Section Chief, Engineering Division, McCook Field, set ten Federation Aeronautique Internationale (FAI) World Air Records and 16 American air records during October 1, 1920 and January 30, 1925. During June 1921, Harris flew the first pressurized aircraft, an experimental D-99-A single-engine biplane. Owing to the circumstance that the pressurization system capability greatly exceeded the outflow valve capability, with no pilot control of cabin pressure, the aircraft cabin became pressurized to 914 m (3,000 ft) below sea level as the aircraft climbed out. The cabin air became hot and Harris was fortunate to get the

airplane unharmed on the ground. Much was learned from this experience. On October 20, 1922, Harris was the first pilot to save his life by parachuting from a Loening PW-2A that broke up in the air (Figure 1-2). He was made member number one of the subsequently famous ‘‘caterpillar club,’’ established by the Irvin Parachute Company. Charles Lindbergh joined the Army as an aviator in training (note: he was already a low-time civilian pilot), Brooks Field, Texas. During training while diving on a target aircraft, another pilot ran into Lindbergh’s craft, the two airplanes becoming locked with one another. Both pilots were in the first class to be issued parachutes, and both parachuted to safety. Lindbergh graduated in March 1925, at the top of his class. Army aviation was underfunded, so he left and joined the Missouri National Guard. Lt. Albert Stevens, a skilled aerial photographer, often flying with Macready, parachuted from a Martin MB2 bomber from an altitude of 7,376 m (24,000 ft) to set a world record over McCook field on June 12, 1922. Capt. Hawthorne C. Gray set unofficial balloon altitude records in 1927. On March 9, 1927, he rose from Belleville, Illinois to an altitude of 8,230 m (27,000 ft) where he passed out due to faulty oxygen equipment and overexertion from emptying ballast bags. Fortunately, the balloon descended and he lived to try again. On May 4, 1927, he lifted off with a new oxygen system and a cord to dump ballast, reaching 12,945 m (42,470 ft). On descent, the balloon began falling at an excessive rate, so he bailed out at 383 m (8,000 ft). Therefore, he did not qualify for an official FAI record, but he was alive. He reported that during the flight he experienced a feeling of detachment, severe chest pains on exertion, and a strong desire to take a nap. On November 4, 1927, Gray went aloft again, reaching 12,192 m (40,000 ft). Unfortunately, his clock froze, he exhausted his oxygen, lost consciousness, and died. On November 5, the gondola was found in a tree near Sparta, Tennessee. Scientists concluded that high-altitude balloon flights should be equipped with sealed cabins. Gen. James H. Doolittle stated during his speech on October 20, 1962, on the occasion of the dedication of the Federal Aviation Agency’s Civil Aeromedical Research Institute new research facilities, Oklahoma City, Oklahoma, that ‘‘The price for almost every advancement in aviation has been high. Progress was frequently bought with someone’s life.’’ McCook Field personnel undertook an agricultural inflight spray program to eradicate the ‘‘catalpa sphinx moth’’ that was wiping out a grove of catalpa trees near Piqua, Ohio. The grove was 32 km (20 mi) north of McCook, and the wood from the trees was used for fence posts and poles. In cooperation with the Ohio Agriculture Experimental Station in Wooster, McCook personnel modified a JN6H (Jenny) to carry powdered arsenate of lead in hoppers that could be released during passes over the trees while flying at an altitude of 6 to 9 m (20 to 30 ft). The aircraft dispensed 79 kg (175 lb) of the insecticide during six passes of 9 seconds each while flying 129 kph (80 mph) on August 3, 1921. Millions of the moth larvae died from eating the dusted leaves.

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FIGURE 1-2 The wreckage of a Loening PW-2A that broke up in the air, October 20, 1922. The pilot, Lt. Harold R. Harris, was the first U.S. Army Air Service flier to save his life by parachuting from his disabled aircraft.

McCook engineer, Etienne Dormoy designed the hopper, John A. Mcready flew the aircraft, and Albert W. Stevens flew alongside to document the dusting. Lt. Harold R. Harris left McCook in 1925 to help found the Huff-Daland crop dusting organization, the forerunner of Delta Airlines, the latter formed in the 1928 to 1929 period from the proceeds of the sale of the crop dusting company. Stevens, in cooperation with the U.S. Department of Agriculture, collected samples of plant disease spores at 10,972 m (36,000 ft) and subsequently at 22,066 m (72,395 ft) on November 11, 1935 using the Explorer II balloon. During 1926, aerial dusting was used by the marines at Quantico to kill mosquitoes (Figure 1-3). During the latter World War II period in the Pacific theatre, updated spraying techniques were used to kill mosquitoes and flies.

medical facility. Selfridge died of a skull fracture. Orville had a fractured left femur, fractured ribs, and other skeletal injuries, but recovered to fly again, although he never completely healed and had lifelong discomfort. Following a repeat demonstration by Orville at Fort Myer in an improved

EARLY CRASH PROTECTION The first fatal crash in powered aircraft activities occurred on September 17, 1908. Orville Wright was demonstrating for the U.S. Army their Wright Model A Flyer at Fort Myer, Virginia, with Lt. Thomas E. Selfridge as passenger. Following some in-flight maneuvers at 30.5 m (100 ft), a propeller fractured. Orville cut power but the propeller caught in the aircraft rigging and the craft crashed in a turn. Selfridge and Orville were extricated and taken to the Post

FIGURE 1-3 The Marine Corps fought a ‘‘battle to death with mosquitoes that besiege the Marine base at Quantico’’ in 1926 using a plane with a special emblem. Shown are MG Elie Cole, Capt. W.M. Garton, USN MC, and Col. T.C. Turner.

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Model A Flyer, on July 30, 1909, the Army Signal Corps agreed to purchase the new aircraft on August 2, 1909. His passenger was Lt. Benjamin D. Foulois. Lt. Henry H. (Hap) Arnold, later a General and Chief of the U.S. Army Air Forces during World War II, elected shortly after the 1908 Fort Myer accident to protect his head during flight by donning his college football helmet. Louis Bleriot, the first to fly the English Channel, on July 25, 1909, began installing restraint systems. Lt. Benjamin D. Foulois, later a U.S. Army Air Service General, wore a trunk strap while flying in San Antonio in 1910. He is quoted as saying ‘‘. . . to keep me in that damn seat during turbulence.’’ Hardy V. Wells, Royal Navy, wrote in 1913 that serious nonfatal injuries as well as fatal injuries could be avoided by having ‘‘some giving material in the position in front of the pilot where the head would strike’’ or by ‘‘a safety belt having shoulder straps’’ (8). His recommendation for elastic belts was not sound. During this time, some used the practice to release the belts just before landing, supposedly to prevent becoming trapped in an airplane that rolls over, catches fire, or prevent being crushed by a pusher-type engine. French automobile builder M.G. Leveau patented in 1903 an automobile seat restraint system involving high-backed seats, lap belts, and adjustable chest cross-straps. Despite early technology, experiences and recommendations about

impact protection, and estimates of 85% to 93% reductions in general aviation aircraft accident fatalities with upper torso restraint, decades would pass before general installation would occur. The 1950s to 1960s research data produced and widely disseminated by John Stapp, John Swearingen, and others, gradually began to be applied by regulatory authorities with respect to civil aircraft as well as automobiles.

EARLY AIR AMBULANCE ACTIVITIES In 1909, U.S. Army Capt. George H.R. Grosman, stationed at Fort Barrancas, Florida, conceived a heavier-than-air aircraft designed to carry patients. With Lt. Albert Rhodes, he designed, built, and flew such an aircraft. The War Department, still apprehensive from the purchase of the 1909 Wright aircraft, did not elect to acquire the air ambulance aircraft. In 1914, Lieutenant Colonel Donegan, Royal Army Medical Corps (MC), proposed to transport medical staff, specialists, emergency equipment, and wounded by airplane. A shortage of aircraft precluded implementation. Captain R.H. Cordner, a year earlier, had recommended such an approach but the approach had been rejected as impractical.

FIGURE 1-4 Airlines were involved in early air ambulance service that existed in the United States, Sweden, and several other European countries in 1929.

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In 1910, Marie Marvingt, a French surgical nurse, balloonist, and airplane pilot, proposed the development of airplane ambulances. In 1912, she ordered an airplane from the Deperdussin Company, but due to failure of the company, the craft was not delivered. She served clandestinely as an infantry soldier in 1914, serving on the frontlines until her superiors discovered that she was a female. She found her way into aerial service, flying as a bomber pilot over Germany. For this, she earned the Croix de Guerre. Throughout the war, she continued to press for air ambulances. Marie Marvingt developed a civil air ambulance service in 1934 for Morocco, with aircraft on skis for landing on desert sand. She was the first woman in France to be awarded the diploma of ‘‘Infirmiere de l’Air’’ (Flight Nurse) in 1935. The first airplane air evacuation in history was from Albania and was carried out in November 1915 by the French Expeditionary Forces and Serbian pilots using French fighter aircraft. The French subsequently ordered aircraft suitable for forward evacuation. In 1947, Italy was the only other country with this evacuation capability. The authorities elsewhere considered such air evacuation to be dangerous, medically unsound, and militarily impossible. Marvingt’s dream of airplane ambulances was fully realized during World War II. Military wounded evacuation numbers reached 1 million/year by the end of the war. Forward air evacuation of wounded soldiers was developed during the Korean War, and the establishment of air ambulances before the Vietnam war reduced the risk to the wounded of dying in combat in that war to less than half that experienced during World War II. Colonial Flying Service offered the first known civilian air ambulance flying service in 1929. A Braniff Airline aircraft is shown in connection with an air ambulance operation in 1929 (Figure 1-4). Boeing Air Transport (predecessor of United Airlines) hired Ellen Church, a registered nurse, as a flight attendant in 1929, introducing a practice that United Airlines followed for some years. The cabin environment of the early unpressurized aircraft, flying in the lower turbulence-prone altitudes, resulted not infrequently in passenger illnesses, especially nausea, vomiting, dizziness, and middle ear discomfort and pain. Nurse flight attendants were especially beneficial in soothing and treating passengers who were so afflicted.

POST–WORLD WAR I AVIATION MEDICINE RESEARCH The years between 1920 and 1935 saw aviation medicine research drop to a very low level. The World War I Air Service Medical Research Laboratory was abandoned in 1920. Longacre’s 1923 selection criteria for candidates for flight training was a recognized accomplishment. In addition, Neely Mashburn’s ‘‘automatic serial-action complex coordinator,’’ (Figure 1-5) developed by May 1931

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FIGURE 1-5 Mashburn’s complex coordinator for determining aptitude for flying training was one of the most significant accomplishments in aviation medicine research between 1920 and 1935.

at the new School of Aviation Medicine (SAM), Randolph Field, Texas, was the most accurate single measure of pilot aptitude at the time. The device was used in World War II to determine reaction times related to pilot aptitude for selection purposes with respect to landing, alcohol effects, and possible age-related aspects. A third accomplishment was that of Dr. David A. Myers, a member of the first formal class of flight surgeons. He worked with William Ocker, a veteran pilot, who was an expert at using the gyroscopic turn and bank instrument developed by Elmer and Lawrence Sperry. He demonstrated through use of the Barany chair, a head-mounted view box, and a stick that the test subject could position to show if a sensation of turning existed, or not, and, if so, the direction of the perceived turn, that the inner ear would be confused in turns should external horizontal reference be lost (Figure 1-6). Ocker and Crane published their book, Blind Flight in Theory and Practice in 1936. Maj. General Harry G. Armstrong, United States Air Force (USAF), MC considered this work on spatial disorientation ‘‘the greatest contribution of medicine to the technical advancement of aviation’’ (9). Two physicians led the revival of aviation medicine in the United States: Harry G. Armstrong and Louis H. Bauer. Between 1939 and 1952, Dr. Armstrong wrote three textbooks on aviation medicine and edited the first textbook on aerospace medicine. Dr. Bauer published a textbook on aviation medicine, 1926, that received attention on both sides of the Atlantic as was the case with Armstrong’s publications (10). Dr. Armstrong felt that flight surgeons were not fully trained until they had completed a 4-month basic course, had 3 years at an Air Corps station, and had 300 hours of flight time. Their duties included diagnosing and treating ailments and trauma cases, as well as performing physical examinations and caring for flyers, ‘‘the essence of aviation

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FIGURE 1-6 A modification of the Barany turning chair has been used to demonstrate spatial disorientation that results from absence of a true horizon or instrument proficiency to tens of thousands of pilots in the United States.

medicine’’ according to Armstrong. In addition, the flight surgeons should continually investigate the effects of flight, and seek remedies for adverse environmental conditions. Armstrong (born on February 17, 1899), De Smet, South Dakota, served as a private in the U.S. Marines during World War I. He attended the premedicine program at the University of Minnesota, and then the University of South Dakota’s medical school, earning the Bachelor of Science in Medicine, 1923. He then matriculated to the University of Louisville, Kentucky, earning the MD degree in 1925. He entered private medical practice in Minneapolis, Minnesota. In 1929, he accepted a commission in the Army Reserve and was assigned to Brooks Field, San Antonio, where he enrolled in the aviation medicine course. A sergeant who was a proponent of dropping soldiers by parachute suggested that a doctor should make a parachute jump to provide a professional assessment of possible associated physiological and psychological problems. This was Armstrong’s first research challenge. Armstrong is quoted by Mr. Bob MacNaughton in a U.S. Air Force News Release, Lackland Air Force Base, 19 May, 1981, as ‘‘So I made the jump and wrote it up. I told them nothing really happens except it really scares the hell out of you.’’ Armstrong, with the concurrence of his wife Mary, was offered and accepted a regular Army commission. Of course, he had to take lessons on riding horses the army way, and

driving a six-mule ambulance. He was assigned in 1931 as flight surgeon to the First Pursuit Group, Selfridge Field, Michigan. His flying time was in Berliner Joyce P-16 twoseat fighter planes. During winter flying, he observed aircrew problems with frostbite and fogged goggles. He wrote to Maj. Gen. Malcolm C. Grow, medical chief of the Army Air Corps, with respect to pilot in-flight medical problems, and received orders on September 15, 1934 to assume the post of consultant to the engineering section, Wright Field. In May 1935, Armstrong succeeded in obtaining approval for the ‘‘Physiological Research Unit,’’ later renamed the Aeromedical Research Laboratory. In June 1936, Armstrong persuaded John W. Heim, PhD, Harvard University, to join the new initiative at Wright Field. Heim and Armstrong proved to be a highly productive research team. Armstrong instituted a series of research activities at Wright Field that included cold chamber studies with various protective clothing for flying (accomplished in the small altitude chamber that was moved from Mineola to Wright Field, and discovered by Armstrong to be underneath a trapdoor in his office), hypoxia altitude chamber studies accomplished in a new altitude chamber commissioned by Armstrong, oxygen mask studies, aeroembolism studies, barotrauma in regard to the middle ear and sinuses, and positive- and negative-G force accelerations using a centrifuge that he and Heim had put together. Additional Armstrong studies included developing a protocol for occupant protection during decompressions should the planned pressurized aircraft be developed. Information on this subject was essentially nonexisting. Therefore, to collect data on this topic, Armstrong placed himself inside an 8-ft long tank that was 2.5 ft in diameter, sealed at ground level pressure. The tank had a series of cork-sealed holes of increasing size. The tank was within an altitude chamber, and, during a series of tests at the simulated altitude of 10,000 ft, Armstrong started by extracting the smallest cork, and progressively worked up to the largest. He reported not being hurt at any of the decompression levels. Armstrong also served as the test subject on a sled that he had built, upon which was a simulated cockpit. He had shoulder harness straps added, started with lowspeed impacts, worked up to higher speed impacts, and demonstrated that an individual’s neck would not be broken by wearing shoulder harnesses under such conditions. This finding dispelled a contemporary myth slowing the acceptance of shoulder harnesses. He also studied helmet requirements for head injury protection during accidents. In 1935, Armstrong made headlines in the Dayton papers by predicting that some day airplanes would fly as fast, or faster than, a 0.45-caliber bullet. Subsequently, on January 24, 1939, H. Lloyd Child power-dived a Curtiss Hawk H-75A-1 over Buffalo, New York, to 966 kph (600 mph) reaching Mach 0.813 at 2,790 m (9,000 ft) altitude. This was in excess of the speed of a black powder pistol bullet. He also discovered resistance by some at SAM with respect to establishing a laboratory at Wright Field as he proposed. As he developed his first textbook, he met

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objections from SAM, the Commandant stating that this was the job of SAM. Numerous reports published by Armstrong along with his associate, Heim, began appearing in 1938, most frequently in the Journal of Aviation Medicine. Armstrong was solely responsible for developing the physiological specifications that were used to design the 1937 military Lockheed X-35, the first practical pressurized aircraft. The same criteria were applied to the subsequent pressurized, tail-wheeled, Boeing 307 Stratocruiser, introduced on December 31, 1938. Both TWA and Pan Am airlines operated these aircraft on long distance flights. These were the first airline aircraft to have an engineer’s position, due to the need to monitor and control the pressurization system. With respect to the new Boothby, Lovelace, and Bulbulian oxygen mask, Armstrong, upon receiving a copy for testing, suggested improvements that included covering the mouth and adding a microphone. In addition, breath moisture tended to freeze shut the metal valves, and Armstrong suggested a fix for this. Adoption of these suggestions led to a very successful mask that the Mayo Clinic patented, with the Air Corps paying royalties as the mask came into wide Air Corps use. Armstrong continued to undertake altitude chamber studies, periodically as a subject. He found that an open container of blood would ‘‘boil’’ at 19,530 m (63,000 ft), an altitude that became known as Armstrong’s Line. In 1939, he authored the textbook, Principles and Practice of Aviation Medicine, a book that proceeded through three updated editions (11). Armstrong with Drs. Boothby and Lovelace received the Collier Trophy in 1940 for their mask development and contributions to aviation safety. In 1949, Armstrong was named Surgeon General of the U.S. Air Force. In this same year, he established the Department of Space Medicine, USAF SAM, Randolph Field, Texas. He retired from the Air Force as a Major General in 1957. In 1982, he received the Edward P. Warner Award of the International Civil Aviation Organization for his singular contributions for pressurized flight. The only other American to have received this award was Charles A. Lindbergh. Armstrong passed away on February 5, 1983, just shy of his 84th birthday. On July 18, 1999, Armstrong was enshrined in the National Aviation Hall of Fame, the second physician to have been so recognized (the first was John Paul Stapp). He left a legacy of peace and wartime contributions in aerospace medicine, including 105 scientific publications, a life that materially contributed to progress in aviation advances and space flight development.

CIVIL AVIATION MEDICINE Louis Hopewell Bauer, born on July 18, 1888, Boston, Massachusetts, saw his first airplane flight as a youth in Boston. His lifelong devotion to aviation began on that occasion (12). With a bachelor of arts degree from Harvard (1909) and a

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doctor of medicine degree from Harvard (1912), Bauer accepted a commission as a first lieutenant in the Army Medical Corps, and attended the Army Medical School from 1913 to 1914. He served on the Mexican border, in the Philippines, and at Kelly Field, San Antonio. In this latter assignment, he served with the first aviation unit and was promoted to the temporary grade of Lieutenant Colonel. He succeeded Col. William H. Wilmer as the Director of the Medical Research Laboratory and led its post–World War I move from Hazelhurst Field to nearby Mitchel Field, Long Island. In March 1921, the laboratory burned down and Bauer oversaw its reconstruction. He established a school for flight surgeons that was designated on November 8, 1922, as the School of Aviation Medicine. In 1922, the Navy began to send medical officers to the school to qualify as flight surgeons. The Navy subsequently established its own flight surgeon school on November 20, 1939, designated as the School of Aviation Medicine, Pensacola, Florida. In August 1925, following 6 years as commandant of the Army School of Aviation Medicine, Dr. Bauer was enrolled in the Army War College, Washington Barracks (the Barracks subsequently became Fort McNair). During this time, he finalized a textbook, Aviation Medicine, published with the authority of the Surgeon General in January 1926 (10). In the summer of 1926, he completed the Army War College and was assigned to Fort Benning, Georgia. On May 20, 1926, President Calvin Coolidge signed the Air Commerce Act. Secretary of Commerce, Herbert Hoover, obtained Bauer’s release from the Army Air Service, and Bauer accepted the position of Director of the Medical Service in the Aeronautics Branch of the Department of Commerce, effective November 16, 1926. He immediately set to work and prepared the first federal civilian medical standards for pilots, Section 66, ‘‘Pilots’ physical qualifications,’’ contained in pages 31 to 32 of the 45-page Air Commerce Regulations, published and effective December 31, 1926, Government Printing Office, Washington, D.C. The physical standards read: ‘‘Private Pilots. Absence of organic disease or defect which would interfere with safe handling of an airplane under the conditions of private flying; visual acuity of at least 20/40 in each eye; (21 mm Hg but 30 mm Hg or with visual field or optic disc changes at any pressure) are treated with either levo-epinephrine, β-blocker, or prostaglandin analog eye drops with remarkable success without creating secondary visual aberrations. Further, a number of new ocular drugs such as topical carbonic anhydrase inhibitors, α-adrenergic agonists, and prostaglandin analogs are now available for treatment of glaucoma and ocular hypertension (86). The laser has also been used to treat glaucomatous conditions. For instance, trabeculoplasty is now often used for openangle glaucoma treatment. Microscopic laser burns are placed in the trabecular meshwork. This enhances the outflow of aqueous and may eliminate the need for ocular medications. In the more rare, narrow-angle glaucoma, the laser can be used to create an iridotomy. Previously, this necessitated surgical iridectomy. Both of these procedures are used in aviators, allowing them to return to full flying duties. Retinal disorders are also seen in the younger patients. Central serous retinopathy, an edema of the macula of unknown origin, plays havoc with a pilot’s stereopsis/depth perception. Fortunately, 97% of these afflicted individuals recovered and were returned to full flight status as noted in a review of USAF aviators with this condition (87). Older flyers may develop macular degeneration that may eventually end their flying careers because presently no effective treatment exists for this condition. A small number of flyers may develop keratoconus or irregular astigmatism, but many of these individuals can be returned to full flight status by the proper fitting of toric or hard-contact lenses. A USAF study showed that 82% of USAF aviators with a diagnosis of keratoconus were returned to full flight status (88). A fair number of individuals have migraine, but only a few flyers complain of it to the aeromedical examiner. The most significant aspect of this condition for flying personnel is developing a central scotoma during an attack or becoming incapacitated by the headache that may follow. Cataracts are commonly seen in the older flying population or as a result of ocular trauma at any age. If the opacity is dense enough, it could affect vision and, therefore, a flyer’s career. Modern surgical procedures and postoperative optical correction either by an intraocular lens placed into the eye at surgery or by a contact lens fitted after surgery may allow many individuals to pass the visual examination and return to flying. Recent data shows that these procedures are quite successful, even in military aviators. In 80 eyes with intraocular lenses, 96% attained 20/20 visual acuity and 86% of those affected were returned to full flight status, 3 being grounded for nonophthalmologic disease, and 3 for ocular complications. The longest follow-up in these patients has been 20 years (89).

Correction of Refractive Errors Standard Techniques Refraction is a procedure used to determine the lens power needed to correct a patient to emmetropia. The refractive

error can be estimated by retinoscopy, which is usually done following the use of cycloplegic eye drops. A manifest or subjective refraction is done with lenses, crossed cylinders, or astigmatic dials, and a third and common way of calculating the refractive error is with a lensometer, which measures the patient’s present spectacle correction. If spectacles were to correct the patient’s vision to 20/20, nothing further would need to be done concerning the refraction. The aviator’s distance refraction changes little during the ages of 20 to 40. After the age of 40, although the error for distance may remain static, a correction for early presbyopia is often necessary. Spherical plus lenses correct the deficient accommodation. Once presbyopia has commenced, the patient needs to be reexamined every 2 years to maintain clear, comfortable near vision. A half-eye spectacle will suffice for the patient with no error in distance vision, but bifocals will be needed to correct the error in those who also require a correction for distance. Trifocals and newer progressive lenses may be helpful to the older pilot needing correction for both near (reading) and intermediate (panel) distances. The use of contact lenses to correct refractive errors began more than 50 years ago. They have found acceptance in civilian aviation and since 1989 have been used in military aviation. After a formidable research effort, the USAF now allows its aviators to use soft contact lenses in place of spectacles. A limited number of tested soft contact lenses are approved for use. Flyers with astigmatism over 0.75 D are fitted with toric soft lenses. The major problem encountered has been the dry cockpit environment. To date, the USAF Soft Contact Lens Program has been a success (90). Hard gas permeable (HGP) lenses are made of silicone-acrylate, and soft contact lenses of hydroxyethylmethacrylate (HEMA) and silicone plastics. The hard lenses are used in a limited manner to correct visual defects, such as irregular astigmatism, keratoconus, and aphakia. The soft contact lens is more comfortable to wear, less time is needed for adaptation, and the soft lens rarely alters the corneal curvature. Soft lenses, however, do have a significant drawback for aviators in that they cannot correct astigmatism of more than 0.75 D. In certain individuals, hard lenses may temporarily or permanently mold the cornea to a different refractive status or curvature. This could fortuitously improve the vision or it could lead to corneal warping and degrade visual acuity.

Newer Techniques for Refractive Error Correction Orthokeratology More than three decades ago, some practitioners began using contact lenses purposely fitted flat to reduce corneal contour and improve uncorrected vision, a procedure called orthokeratology (to straighten the cornea). While this technique can alter the corneal curvature, it is highly unpredictable and not permanent (91). It requires the use of so-called retainer contact lenses to maintain the effect; however, most corneas revert to their original curvatures and refractive errors in several weeks once these lenses are discontinued. Regrettably, this procedure can cause

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‘‘with-the-rule’’ astigmatism that mimics keratoconus or even a decrease in vision from corneal scarring. Refractive Surgery CRS procedures have now been developed to more permanently alter the refractive status of the eye. Although, most of these procedures were developed to correct myopia, CRS techniques are now also available to correct hyperopia and astigmatism. One of the earliest myopic procedures was a rediscovered technique from the 1950s called radial keratotomy (RK). RK involves making four or more radial incisions in the corneal stroma down to the depth of Descemet’s membrane, reaching radially to the limbus, but sparing the central 3 to 4 mm optical zone over the pupil. These weakening incisions flatten the central cornea, thereby decreasing the amount of overall myopia. As with orthokeratology, corneal response to RK incisions is variable and unpredictable; but much more permanent (92). Although rarely performed now, pilot aspirants in the past willingly underwent RK hoping to qualify for aviation careers. Presently, most military services do not allow RK because of reduced corneal integrity, long-term instability (progressive hyperopic shift), daily fluctuations in vision, glare, altitude effects and because even longer-term consequences of RK remain unknown (93,94). Fortunately, RK has been almost completely replaced by newer and more effective CRS procedures in most countries. More recently, newer forms of CRS have emerged using lasers, such as the 193 nm ultraviolet excimer laser, to ablate and flatten the central cornea. Myopic procedures using this laser can be categorized into surface ablations, most notably PRK and its variants [laser epithelial keratomileusis (LASEK) and epi-LASIK], or deeper ablations performed beneath a hinged corneal flap, known as laser in-situ keratomileusis (LASIK). LASIK flaps can be created with a mechanical microtome, or more recently, using a femtosecond infrared laser (IntraLase) (95,96). In general, corneal haze following CRS appears more of a problem with PRK than LASIK. However, the LASIK corneal flap never heals completely and remains chronically unstable, which may be problematic in certain vocations and occupations. For example, incidental levels of corneal trauma have been shown to dislocate LASIK flaps up to 6 years after the procedure, so far (97). In addition, altitude, windblast, water-blast, and G effects remain significant potential threats to LASIK eyes long-term. Adequate aeromedical studies to investigate these LASIK concerns have not yet been done. Despite this, LASIK has become more popular than PRK because of faster results, less corneal haze, and reduced ocular pain in the immediate postoperative period. However, this gap is narrowing because newer analgesics have made PRK virtually pain-free and advanced wave-front analysis (custom-CRS) appears more effective with surface ablations, making custom-PRK a potentially more suitable procedure for the aviator (98). Both PRK and LASIK are mainly used for the correction of myopia up to −8.00 D, but more recently also for treating hyperopia and astigmatism. Complications,

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however, increase as the amount of myopia increases. Other hyperopic CRS techniques, for example laser thermal keratoplasty, use IR lasers to induce central corneal steepening from circumferential thermal burns. Nonlaser CRS techniques, such as intrastromal corneal implants (Intacs) and implantable intraocular contact lenses (ICLs) exist, but each of these has more limited application because aeromedical uncertainties will limit their indications and appeal (99–101). The literature reports that 89% to 98% of low myopes obtain 20/40, and 65% to 80%, 20/20 or better visual acuity, following CRS (102). Accuracy to within ±1.00 D varies between 75% and 95%, depending on amount of preoperative myopia (103). Questions remain, however, whether the postoperative goal of 20/20 is adequate, given preoperative best-corrected means of 20/13 in trained and applicant aircrew populations around the world (104–106). Postoperative corneal haze and induced higher-order wave aberrations from CRS can affect the overall quality of vision and cause haloes and glare, especially under low light when the pupil dilates. Contrast sensitivity function, the ability to see under less-than-ideal conditions, has also been shown to be decreased even beyond 12 months following both procedures. Predictability for aviation remains a problem. If one were corrected to within the ‘‘1.00 diopter’’ accuracy, the 20/20 uncorrected visual acuity desired for a pilot would not be met. Finally, the possibility of regression and the risks of retinal detachment long-term remain after CRS. Regardless, PRK and LASIK have been approved by the U.S. Federal Drug Administration (FDA), FAA, and are now allowed by the U.S. military for most career fields to include flying. Continued studies, however, are needed to determine the full operational impact of modern CRS on aviators, particularly for military aviation.

PROTECTION OF VISION Ocular Protective Materials Since June 1972, all spectacle lenses used in the United States have had to be impact resistant by an FDA ruling. Impact resistant does not mean that they are unbreakable, just that a glass lens must withstand a 5/8-in. diameter steel ball dropped on it from a 50-in. height. Glass lenses are hardened to withstand the drop-ball test by heat or chemical tempering. A plastic, allyldiglycol carbonate (CR-39) lens may also be used in place of glass. A transparent plastic polycarbonate (Lexan) is being used in helmet-mounted visors and as a cockpit transparency that is strong enough to withstand bird strikes. Bird strikes are hazardous to low-flying, high-speed aircraft. The combination of a multilayered polycarbonate windshield and a visor of similar material for the aviator’s helmet have markedly improved the protection against this lethal hazard. A dual-visor system, one clear and one tinted, allows for maximum protection under all flight conditions. Polycarbonate lenses are now available in lenses to correct

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refractive errors. For sports and occupational activities, polycarbonate can be used as a protective goggle over ordinary spectacles, or can be placed directly into spectacle frames, thereby correcting the visual acuity and protecting the eyes. This material also has a secondary benefit in that it protects against ultraviolet light. It begins to transmit at 385 nm, blocking all shorter wavelengths. However, it is susceptible to scratching and costs more (107).

Filters and Sunglasses The extent and effects of electromagnetic energy (light) on the eye have been previously discussed. As noted, light intensities in the aviation environment can be up to 30% higher than on earth. Abiotic ultraviolet radiation (200 to 295 nm) is filtered by the atmosphere but does begin to become significant at high altitudes. Ultraviolet radiation 300 to 400 nm, which is abundant on Earth, is now reputed to have some damaging effect on the human lens following long-term, chronic exposure and may be linked to macular degeneration. IR radiation above 760 nm is a contributor to solar and nuclear retinal burns. Sunlight falling on the earth is composed of 58% IR energy (760–2,100 nm), 40% visible light (400–760 nm), and only 2% ultraviolet radiation (295–400 nm). At high altitude, ultraviolet radiation may be as high 4% to 6% and makes up 8% to 10% of the solar energy spectrum in space. Sunglasses can protect the aviator from excessive and harmful electromagnetic energy. The ideal sunglasses for the aviator should do the following: 1. 2. 3. 4. 5. 6. 7. 8.

Correct refractive errors and presbyopia Protect against physical energy (wind or foreign objects) Reduce overall light intensity Transmit all visible energy but attenuate ultraviolet and IR radiation Not distort colors Not interfere with stereopsis (depth perception) Be compatible with headgear and flying equipment Be rugged, inexpensive, and need minimal care

Five types of sunglasses are now in common use: colored filters, neutral filters, reflecting filters, polarizing filters, and photochromic filters. They all allow only a certain percentage of the total amount of incident light to get through to the eye but produce this effect in different ways. The colored, neutral, polarizing, and photochromic filters do this by absorbing some of the light and allowing the rest to pass. Spectral filtering is achieved in glass lenses by adding specific chemicals to the melt, producing a through-and-through tint. The anterior surface of the glass lens also may only be tinted, but this method is subject to scratching. Plastic lenses are usually dipped into dyes to produce their filtering effect. Colored filters have the disadvantage of altering the color of viewed objects and may reduce color discrimination of color vision–deficient persons. Neutral filters adequately reduce the amount of light. Mainly, they do not distort colors and most will adequately eliminate excessive IR and ultraviolet radiation.

Reflecting filters can be coated uniformly. They eliminate the ultraviolet and IR energy; however, this type of coating scratches and peels easily and gives a greenish tint to objects. Polarizing filters reduce glare off water or highways. For the aviator, they can cause a problem, such as blind spots in windshields and canopies, due to stress polarization induced by the canopy, matching that in the spectacles. Plastic polarized filters scratch easily and, when laminated in glass, are expensive and heavy. Photochromic filters (variable light transmission) are photodynamic lenses that vary in intensity in response to the ultraviolet content of the incident light. Some flyers may find the darkest density sufficient; however, for aviation use, the range of transmission variation is not adequate. The darker lenses remain too dark in the ‘‘open’’ state, and the lighter lenses are not dark enough at their maximum density (108). Density and cycling time can be reduced, particularly in hot and low-ultraviolet environments, such as inside automobiles or cockpits, where ambient light is altered traversing another transparency. This is shown in Figure 14-29, which also compares these lenses with other filters.

Selection of Sunglasses for the Aviator The lens material should be CR-39 or polycarbonate plastic or impact-resistant glass. After much experimentation, a 15% neutral density–transmitting lens probably represents the best all-around compromise for aviation. Some individuals prefer a 25% transmitting lens for daily use (e.g., driving or sports) but switch to the 15% transmitting lens for aviation use. The lens should have a fairly flat transmission curve in the visible energy range to preserve normal color vision but attenuate the ultraviolet and IR radiation. An ideal transmission curve is shown in Figure 14-30. The difference in overall transmission between the two spectacle lenses should not be greater than 10%; otherwise, this disparity will induce the Pulfrich effect as that may Transmittance range (%) of sunsensor lenses (2.0 mm) compared to other filters and clear lenses Photogray – 77 F°

Photosun – 77 F° 100% 96% Clear lenses 80 65% Fashion tint 60

40 35% Light sunglasses 20 15% Dark sunglasses 0.0

FIGURE 14-29 Effectiveness of various tints of lenses in reducing light transmission.

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N-15 Glass lens Ultra violet

Visible spectrum

Infra red

Percent transmission

100

40

20 10

200

300

400

500

600

700

800 1,400 1,500 1,600 1,700 1,800 1,900 2,000

Wavelength (nm)

FIGURE 14-30

Idle transmission curve for sunglasses for the aviator.

degrade stereoscopic vision and depth perception. When sufficient overall light intensity is present, such as in daylight, visual acuity through 15% neutral density, transmitting lenses will be as good as in the eye lane without filters. Under low-light levels, such as at dawn or evening and on dark cloudy days, sunglasses reduce both contrast sensitivity and central visual acuity and, therefore, should be removed. Much has been said concerning certain selective waveband filters known as blue blockers that cut off all ultraviolet and blue portion of the spectrum. Cutting out any of the colors in the spectrum is not desirable in aviation. The aviator’s ‘‘neutral density’’ sunglass lenses allow all colors through and effectively reduce ultraviolet light as well. Under extraordinary conditions, electromagnetic energy may reach such a magnitude that ordinary protective devices will not be adequate. Such tremendous amounts of energy can be released during a nuclear detonation or packaged in a laser beam making protection of the eye against these energy sources is a must; otherwise, permanent injury to the eye will ensue (109).

Nuclear Flash Protection In spite of the fact that the nuclear weapons threat has been dramatically reduced, it still remains; therefore, the material to follow has more than an historical interest. The eye is more susceptible to injury from nuclear explosions at far greater distances than any other organ or tissue of the body. When a pupil of a given size is exposed to a nuclear detonation at a given distance, it will result in a certain amount of energy being distributed over the image on the retina. When one doubles the distance from the detonation, the amount of energy passing through the same size pupil will be only one fourth as great. The image area on the retina, however, will be only one fourth as large; therefore, the energy per unit area will remain constant irrespective of the distance from the detonation except for the attenuation due to the atmosphere and ocular media. The potential danger of flashblindness and chorioretinal burns resulting from viewing nuclear fireballs remains a threat to aircrew members.

During daylight, with high-ambient illumination and through a small pupillary diameter, the retinal burn and flashblindness problems are greatly diminished. At night, with a large pupil, protection is a must. Many different ideas for eye protection have been advocated. Fixed-density filters, on either the pilot or the windscreen, electromechanical and electro-optical goggles, explosive lens filters, and phototropic devices have been developed. The sum total of all this work is that a 2% transmission-fixed filter, gold-plated visor gives adequate protection against retinal burns and reduces flashblindness to manageable proportions during daylight. This filter, however, cannot be used at night. Another aid, a readily available countermeasure to flashblindness, day or night, is the ability to raise instrument panel illumination by auxiliary panel lighting to 125 ft-c. This increased illumination significantly reduces visual recovery time. The ideal ‘‘omni’’ protector against nuclear flash is still being sought. The most recently developed material for protecting against nuclear flash is a transparent ferroelectroceramic material (lead lanthanum zirconate titanate, PLZT) placed between crossed polarizers, as shown in Figure 14-31, reacts to the light energy of detonation within 50 to 100

PLZT Ceramic Crossed polarizers

Incident light

Control circuit Photodiode (1 of 5)

FIGURE 14-31 Flash-blindness-protective goggles. PLZT, lead lanthanum zirconate titanate.

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milliseconds, reaching an optical density of 3. Its largest drawback is that in its open state, it transmits only 20% of the light. It may also be of interest that the 2%-transmitting gold-plated visor, developed at the USAFSAM for protection of aircrew against the flash of enemy nuclear weapons, was never used for that purpose. Instead, it was used as the outermost visor by astronauts in the peaceful exploration of the moon and space.

Laser Eye Protection Lasers (light amplification by stimulated emission of radiation) produce monochromatic, coherent, collimated light. The laser beam diverges little, so that the energy of the beam decreases only minimally with increasing distance from the source. Laser energy is capable of severely injuring tissue in the eye that absorbs the beam energy. For example, Argon (480 nm), frequency-doubled YAG (532 nm), ruby (693 nm), neodymium (1,064 nm) lasers can injure the retina and choroid because these tissues absorb these wavelengths. Laser classification has been recently revised by the American National Standards Institute standard Z-136.1 as follows (110):

Laser Class

Class 1 Class 1M Class 2 Class 2M Class 3R (visible) Class 3R (nonvisible) Class 3B Class 4

Allowed Continuous Wave (CW) Laser Power

40 µw for blue and 400 µw for red Same as class 1 1 mW Same as class 2 5 mW 5 times class 1 500 mW Not limited

The military applications of lasers are increasing in the areas of target ranging and illumination. Pilots themselves are not usually at hazard from their own laser beams, but technicians and others working with such instruments should wear protective goggles or visors with an optical density that is considered safe at the laser wavelength being employed. The laser itself may be used as a weapon. Here it would be helpful if one knew the threat and used a filter to protect from that waveband. Ideally, an agile filter would be in the open state but close down when struck by a laser beam. Unfortunately, this type of protection is as yet not available. Another area of interest especially for aviation is the use of lasers around aiports. The International Civil Aviation Organization (ICAO) recently adopted an international standard that controls lasers emitted in and around international airports (111). Those restrictions were based on earlier FAA limitation established to protect U.S. airports from laser beam intrusions (Figure 14-32). The medical management of laser eye injuries is fully covered in a USAFSAM technical report, TR-88-21 (112). Injuries to the

Laser beam− sensitive flight zone

Laser beam critical flight zone

+

19 500 m

Aerodrome reference point

Laser beam free flight zone

To be determined by local aerodrome operations

Note — The dimensions indicated are given as guidance only.

FIGURE 14-32

Protected flight zones.

external eye, cornea, and lids can be treated. Retinal injuries affect vision, depending on the energy density absorbed by the retina and, more importantly, the location of the injury on the retina. A direct hit to the fovea markedly reduces central vision and is permanent, with little recovery of function. Other safety factors should also be considered, such as educating the worker in laser safety, not looking at the laser beam, examining for reflective materials in the laboratory or shop, posting warning signs, and operating a laser in welllit rooms when possible (small pupils). Laser-safe working distances, the selection of protective materials, and safety programs are becoming quite complicated and involved for the flight surgeon to manage alone. One should have help from a bioenvironmental engineer or health physicist when possible. The flight surgeon or aeromedical examiner, however, is responsible for setting up and performing ocular surveillance programs. Minimally, the examiner should give laser workers complete ocular examinations before they begin their assignments or employment. This should include a distance and near-central visual acuity examination, both corrected and uncorrected, an Amsler grid examination, color vision and an ophthalmoscopic examination of the fundus, with special attention to the fovea (any anomalies of the fundus should be meticulously recorded or a retinal photograph taken). A similar examination should be performed at the termination of the assignment or employment. Annual ocular examinations are not considered necessary; however, anyone working with lasers who has an ocular complaint or claims to have been injured by a laser should be examined and the complaint evaluated (113). As stated at the beginning of this chapter, vision plays the most important role in data gathering for humans; anything affecting vision is significant for the aviator. The flight

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surgeon and aeromedical examiner who care for aviators and attempt to increase their effectiveness should pay special attention to the vision and visual systems of aviators. Instantaneous, clear vision assures us of receiving uncluttered and accurate visual data into our mental computers. The integrating and processing of this information after its reception is in the domain of the central nervous system and is enhanced by training and education of the aviator. If inaccurate or incomplete visual information were received, however, we would almost be assured of failing to perform the task. With the time element for decision making becoming ever shorter in modern aviation, there is added impetus to look carefully at the visual system. This chapter examined the physical, physiologic, medical, and bioengineering aspects of vision. With visual selection and enhancement by visual aids, the aviator’s visual range has been extended, thereby giving more time for reaction and decision making. After selecting aviators with exceptional visual capabilities, it is important to employ the techniques for maintaining and protecting their vision and visual apparatus so that they enjoy full flying careers. Ophthalmology and the other visual sciences are now complex, scientific specialties. This chapter, however, has attempted to give information and data in a manner that is understandable and useful for all physicians and others interested in the subject.

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61. Hansen E. The disturbance of colour vision after sunbathing. In: G Verriest, ed. Colour vision deficiencies V. Bristol, England: Adam Hilger Ltd, 1980. 62. Tso M, Wordford MS. Effect of photic injury on the retinal tissue. Ophthalmology 1983;90:952–963. 63. Fishman GA. Ocular phototoxicity: guidelines for selecting sunglasses. Surv Ophthalmol 1986;31(2):119–124. 64. Ham WT, Ruffolo HA, Mueller HA, et al. The nature of retinal radiation damage: dependence in wavelength, power level, and exposure time. Vision Res 1980;20:1105–1111. 65. Sliney D, Wolbarsht M. Safety with lasers and other optical sources: a comprehensive handbook. New York: Plenum Press, 1982:251– 252. 66. Jaeger W, Krastel H. Colour vision deficiencies caused by pharmacotherapy. Colour vision deficiencies VIII. Martinus Nijhoff/Dr W. Junk Publishers, 1987. 67. Fraunfeld FT, Meyer SM. Drug induced ocular side effects and drug interactions. 3rd ed. London: Lea & Febiger, 1989. 68. Lakowski R, Morton A. Acquired colour losses and oral contraceptives. Mod Prob Ophthal 1978;19:314–318. 69. Mahon LE, Jacobs RJ. Electronic flight information displays and colour defective observers. Clin Exp Optom 1994;74:196–203. 70. Cole BL, MacDonald WA. Defective colour vision can impede information acquisition from color coded video displays. Victorian College of Optom, Report No. 3 to the Dept. of Aviation Melbourne, Australia, 1986. 71. Cole BL, MacDonald WA. Defective colour vision can impede information acquisition from redundantly colour coded video displays. Ophthalmic Physiol Opt 1988;8:198–210. 72. Mertens HW, Milburn NJ. Performance of color-dependent tasks of air traffic control specialists as a function of type and degree of color vision deficiency. Report DOT/FAA/AM-92/28. Washington, DC: Federal Aviation Administration, Office of Aviation Medicine, 1992. 73. Christ RE. Review and analysis of color coding research for visual displays. Hum Factors 1975;17:542–570. 74. Bergman H, Duijnhouwer F. Recognition of VDU presented colours by colour defective observers. In Proc, 24th Annual Meeting Human Factors Soc, The Human Factors Soc, Santa Monica, 1980:611–615. 75. Andresen S. Signal recognition performances of color vision normals and color defectives related to work at a multicolor screen. Bremen, Kiel, 1992. 76. Mertens HW, Milburn NJ. Validity of clinical color vision tests for air traffic control. Aviat Space Environ Med 1998;69(7):666– 674. 77. Kuyk TK, Veres IIIJG, Lahey MA, et al. The ability of protan color defectives to perform color-dependent air traffic control tasks. Am J Optom Physiol Opt 1986;63:682–686. 78. Cole BL. The handicap of abnormal color vision. Clin Exp Optom 2004;87:4–5. 79. Welsh KW, Vaughan JA, Rasmussen PG. Aeromedical implications of the X-chrome lens for improving color vision deficiencies. Aviat Space Environ Med 1979;50:249. 80. Wulfeck JW, Weisz A, Raben M. Vision in military aviation. WADC Technical Report 58–399. Wright Air Development Center, Wright-Patterson AFB, Ohio, 1958. 81. Provines WF, Kislin B, Tredici TJ. Multiple images in the F/FB111 aircraft windshield: their generation, spatial localization, and recording. SAM-TR-77-32, Brooks Air Force Base, Texas: United States Air Force School of Aerospace Medicine, 1977. 82. Sanders DR, Koch DD. An atlas of corneal topography. Thoroughfare: Slack, Inc, 1993. 83. Peters DR, Green RP Jr. The pigmentary dispersion disorder in USAF aviators. Aviat Space Environ Med 1992;63:1049–1053. 84. American Academy of Ophthalmology. American Academy of Ophthalmology Optic nervehead and retinal fiber layer analysis. Ophthalmology 1999;106(7).

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85. Tredici TJ. Screening and management of glaucoma in flying personnel. Mil Med 1980;145:1. 86. Serle JB, Podos SM. New therapeutic options for the treatment of glaucoma. Focal Points 1999;XVII(5). 87. Green RP Jr, Carlson DW, Dieckert JP, et al. Central serous chorioretinopathy in US Air Force aviators: a review. Aviat Space Environ Med 1988;59:1170–1175. 88. Carlson DW, Green RP Jr. The career impact of keratoconus on Air Force aviators. Am J Ophthalmol 1991;112:557–561. 89. Tredici TJ, Stern C, Burroughs J, Ivan DJ. Poster: cataract surgery in USAF pilots. American Academy of Ophthalmology annual meeting. Atlanta, 1995. 90. Dennis RJ, Apsey DA, Ivan DJ. Aircrew soft contact lens wear: a survey of USAF eye care professionals. Aviat Space Environ Med 1993;64:1044–1047. 91. Tredici TJ. Role of orthokeratology: a perspective. Ophthalmology 1979;86:698. 92. Rowsey JJ, Balyeat HD. Preliminary results and complications of radial keratotomy. Am J Ophthalmol 1982;93:437. 93. Waring GO III. Focal points: clinical modules for ophthalmologists. Vol. 10, No. 5. San Francisco: American Academy of Ophthalmology, 1992. 94. Waring GO III. Radial keratotomy for myopia. In: Focal points: clinical modules for ophthalmologists. Vol. 10, No. 5. San Francisco: American Academy of Ophthalmology, 1992. 95. Kezerian GM, Stonecipher KG. Comparison of the IntraLase femtosecond laser and mechanical keratomes for laser in situkeratomileusis. J Refract Surg 2004;30:804–811. 96. Durrie DS, Kezerlan GM. Femtosecond laser versus mechanical keratome flaps in wavefront-guided in situkeratomileusis. J Cataract Refract Surg 2005;31:120–126. 97. Landau D, Levy J, Solomon A, et al. Traumatic corneal flap dislocation one to six years after LASIK in nine eyes with a favorable outcome. J Refract Surg 2006;22(9):884–889. 98. Guttman C, Talsman J, McDonald M. Can future patients expect to see better than 20/20? Ophthalmol times 2001;26(5):21.Mar 99. Vukich JA, Ticlittom ISG. U.S. Food and Drug Administration clinical trial of the implantable contact lens for moderate to high myopia. Ophthalmology 2003;110:255–266. 100. Rapuano CJ, Sugar A, Kolch DD, et al. Intrastromal corneal ring segments for low myopia. Ophthalmology 2001;108:1922– 1928. 101. Holmes-Higgin DK, Burris TE. Corneal surface topography and associated visual performance with Intacs for myopia: phase III clinical trial results. The Intacs Study Group. Ophthalmology 2000;107:2061–2071.

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102. Ivan DJ, Tredici TJ, Perez-Becerra J, et al. Photorefractive keratectomy (PRK) in the military aviator: an aeromedical perspective. Aviat Space Environ Med 1996;67(8):770–776. 103. Diamond S. Excimer laser photorefractive keratectomy (PRK) for myopia—present status: aerospace considerations. Aviat Space Environ Med 1995;66:690–693. 104. Ohlsson J, Villareal G. The ‘‘20/20’’ standard. Acta Ophthalmol Scand 2005;83(4):487–491. 105. Velasco e Cruz AA. Historical roots of 20/20 as a (wrong) standard value of normal visual acuity. Optom Vis Sci 1990;67:661. 106. Frisen L, Frisen M. How good is normal visual acuity? A study of letter acuity thresholds as a function of age. Albrecht Von Graefes Arch Klin Exp Ophthalmol 1981;215:149–157. 107. Miller D. Optics and refraction. New York: Gower Medical Publishers, 1991:10–13. 108. Welsh KW, Miller JW, Shacklett DE. An acceptability study of photochromic lenses. Optom Wkly 1976;21:16–21. 109. Byrnes JA, Brown DVL, Rose HW, et al. Chorioretinal burns produced by an atomic flash. Arch Ophthalmol 1956;55:351. 110. American National Standards Institute. American national standards for the safe use of lasers. New York: American National Standards Institute, ANSI Z136.1 1976. 111. International Civil Aviation Organization. Manual on laser emitter and flight safety, First Edition. International Civil Aviation Organization. 2003. 112. Green RP Jr, Cartledge RM, Chaney FE, Menendez AR. Medical management of combat laser eye energies. USAFSAM-TR-88-21, 1988. 113. Air Force Occupational Safety and Health. Air Force Occupational Safety and Health (AFOSH) Standard 161-10, Health Hazards Control Laser Radiation. Washington, DC: Department of the Air Force, 1980:23–24.

RECOMMENDED READINGS Gregory RL. Eye and brain, 4th ed. Princeton: Princeton University Press, 1990. Lerman S. Radiant energy and the eye. New York: Macmillan, 1980. Michaels DD. Visual optics and refraction. St Louis: Mosby, 1985. Newell FW. Ophthalmology, principles and concepts, 8th ed. St Louis: Mosby–Year Book, 1996. Pitts DG, Kleinstern RN. Environmental vision. Boston: ButterworthHeinemann, 1993. Yanoff M, Duker JS. Ophthalmology. St Louis: Mosby, 1999.

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Otolaryngology in Aerospace Medicine James R. Phelan

INTRODUCTION The ear, nose, and throat (ENT) area, like many others, contains several structures that must be functioning properly for the safe performance of flying duties. It is safe to say that when these functions are impaired or exaggerated, such as when the Eustachian tube is blocked or the labyrinth is sending conflicting signals to the central nervous system (CNS), an aircrew member may become suddenly and completely incapacitated. Some ENT conditions may be permanently disqualifying for flight, but most are either self-limited or reversible with proper treatment. Fortunately, it is uncommon for a trained aviator or an astronaut to be permanently grounded as a result of an ENT illness or condition.

Functional Anatomy and Physiology The Ear and Hearing Because adequate hearing is essential to the safe operation of any aircraft or spacecraft, it is of the utmost importance that existing hearing be preserved, and that any treatable hearing loss be considered for treatment. For any sound to be heard normally, a complex chain of events must happen, and any interruption in this chain can result in diminished or absent hearing. Perception of sound involves both physical and electrochemical processes. It begins with the collection of sound pressure waves by the external ears, which provide a small amount of amplification, and more importantly, localization of sounds in space. Localization is possible because sound waves reach each ear at slightly different times, at slightly different volumes, and with slightly different resonances, depending on the position of the head. Tiny movements of the head help in this localization. Much of this localization is lost when wearing headsets, although sophisticated acoustic engineering can restore some of this localization. Once the sound waves have entered the gently curved external ear canal, they impinge on the tympanic membrane (TM) causing physical 380

vibration of the TM and its three attached middle ear ossicles. The malleus is embedded within the midportion of the TM, the incus provides a bridge from the malleus to the stapes, and the stapes inserts into the oval window, which is the middle ear’s interface with the inner ear. The area of the TM is approximately 20 times the area of the oval window, providing mechanical amplification of the sound waves. In addition, the ossicles themselves are levered in such a way as to provide further mechanical advantage to the system. Absence of the TM and/or ossicles invariably leads to a rather large conductive-type hearing loss. Although this may occur congenitally, in the trained aircrew it is usually the result of trauma, infection, or surgery. At the oval window, the stapes footplate is in direct contact with the perilymph of the inner ear and sound vibrations are transmitted through this fluid to the neurosensory hair cells of the cochlea. Each of these cells is ciliated, and the cilia deform in response to the propagating vibratory wave. The amplitude of this wave is interpreted as volume, whereas the frequency is sensed as pitch. Different pitches are sensed by hair cells in different areas of the cochlea. As the cilia deform, neurotransmitters are released and action potentials are generated. These action potentials are carried to the CNS by the eigth cranial nerve through the brainstem to the temporal cortex, where they are interpreted as sound.

Balance The sense of balance is achieved through a complex interaction between the eyes, the cerebellum, skin, muscle and joint proprioceptors, and the vestibular portion of the inner ear. When any one of these components is compromised, it is possible to compensate for its loss. For instance, if the eyes are closed but all other balance systems are normal, we can usually remain upright and even walk fairly normally. However, when two or more systems are impaired, the sense of balance can be seriously degraded. This discussion will only focus on the balance function of the inner ear.

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Each inner ear has two types of ‘‘accelerometers,’’ the ampullae of the semicircular canals, which sense angular acceleration and the maculae of the utricle and saccule that sense linear acceleration. There are three semicircular canals in each ear, oriented at right angles to each other, allowing them to sense acceleration in three different axes. These axes are analogous to the three basic axes of aircraft maneuvering, yaw, pitch, and roll. The opposite ear senses the same motions in a complementary manner, and together they can sense complex combinations of these three basic motions. There are ciliated cells within the ampullae, and they deform in response to the motion of fluid within the canals, thereby generating action potentials that are then sensed as motion. However, the canals have a rotational threshold of approximately 3 degrees/s. Motion below this threshold is not sensed, which has important implications for aviation. For example, it is possible for an aviator to have the aircraft slowly roll and descend without him or her being aware of any sensation whatsoever. If this occurs in instrument meteorologic conditions and the gauges have not been monitored carefully, control of the aircraft may be lost due to spatial disorientation and controlled flight into terrain. Linear acceleration, such as felt during a catapult launch or when extending the speed brake, is sensed by the utricle and saccule. Gravity is also a linear acceleration, although we are generally unaware of it unless its forces on the body are altered or eliminated such as during aerobatics or space flight. Inner ear inputs to the vestibular system help control the many activities in which we engage, from getting out of bed in the morning to performing competitive gymnastics. Through these inputs, the semicircular canals help in keeping our eyes focused on a target when our head is moving, and they help prevent falling to the ground when we stumble. However, the aerospace environment can challenge these inner ear functions, so it is important to be aware of their limitations.

The Nose and Sinuses The nose and the paranasal sinuses may be considered as a unit because normal sinuses are aerated, and they communicate directly with the air in the nasal cavity. Both structures are lined with ciliated mucosa that normally produces a thin mucus blanket that is slowly transported by ciliary action toward the nasopharynx where it is eventually swallowed. Although there is no obvious reason why sinuses exist, the nose itself has four clearly important functions in addition to allowing the passage of air: humidification, warming, cleansing of inspired air, and olfaction. In addition, the nose and sinuses together lend a characteristic resonance to speech that can change temporarily during the course of a sinonasal infection. Within the nasal cavity, there are three pairs of turbinates: inferior, middle, and superior. The inferior turbinates are highly vascular and can readily engorge with blood in response to inflammatory or autonomic stimuli. The middle turbinates are smaller and not quite

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as vascular, but are also capable of some swelling, and can develop polypoid degeneration in response to assorted irritants such as nasal allergens or chronic purulent sinus drainage. Because of their location near the ostia of the maxillary, frontal, and anterior ethmoid sinuses, swelling of the middle turbinates has a greater effect on sinus aeration and drainage than does swelling of the inferior turbinates, which contribute more to symptomatic congestion. The superior turbinates are small, difficult to see on routine examination, and rarely play a role in nasal or sinus obstruction. All of the turbinates taken together create a large surface area, allowing for inspired air to interact more thoroughly with the mucosa. As air enters the nose and reaches the turbinates, its flow becomes somewhat turbulent. This allows for maximum contact between air and mucosa, enhancing the abovementioned nasal functions. The normal rhythmic back-andforth nasal airflow also creates a small amount of airflow into and out of the sinuses, thereby maintaining normal oxygen partial pressures within. Well-aerated sinuses with functioning ciliated mucosa are not prone to infection. In contrast, interruption of this airflow coupled with compromise of ciliary action can lead to mucus stagnation and an increased likelihood of infection. Conditions that cause injury to the mucosa and/or blockage of the ostia and nasal cavity favor the development of bacterial sinusitis. These include viral upper respiratory infections (URIs), significant allergic rhinitis (particularly, when accompanied by nasal polyps), overuse of topical decongestant sprays, and even inhalation of excessively dry air. Although decongestants and dry air do not by themselves cause sinusitis, they can lead to thickening and crusting of nasal mucus secretions, which can hinder the migration of the mucus blanket, thereby increasing the chances of stagnation and bacterial growth. It is important to maintain adequate hydration when exposed to very dry air, and the additional use of saline nasal sprays or gels can be helpful.

Swallowing and the Eustachian Tube The Eustachian tube is the only route for air to enter and leave the middle ear when the TM is intact. The Eustachian tube also provides a drainage route for mucus secreted by the middle ear mucosa, and because it is normally closed at rest it protects the middle ear from pharyngeal secretions and dampens the perception of one’s own voice. Normal transmission of sound from the TM and ossicles to the oval window depends on a middle ear filled with air at ambient pressure, and any change from that state can result in conductive hearing loss. The air cells within the mastoid bone communicate with the middle ear and provide an additional volume of air that can briefly act as a buffer against potentially painful changes in ambient pressure, but the Eustachian tube is always the primary route for pressure equalization. Middle ear ventilation usually happens without our awareness, because the Eustachian tube opens chiefly by contraction of the tensor veli palatini muscle during swallowing and yawning; this opening allows a small volume

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of air to pass. This ventilation must be done periodically, for if the Eustachian tube does not open, gases in the middle ear will equilibrate with lower partial-pressure gases in the mucosa, causing a slow decrease in middle ear pressure, and possibly leading to an effusion. As the ambient pressure decreases during ascent in an aircraft, the middle ear pressure becomes relatively higher, and the Eustachian tube in almost every case will vent passively. This venting can be facilitated by a quick swallow or yawn, but it is generally not necessary. However, during descent, when increasing ambient air pressure begins to push the TM inward, the Eustachian tube must be actively opened by performing some type of maneuver. If nothing is done, significant pain invariably results, and if the pressure differential is high enough a middle ear effusion will occur. This will be discussed further in the section Barotitis Media.

The Upper Airway The oral and nasal airways are equipped with structures that can increase resistance to inhalation and exhalation, thereby helping to maintain lung compliance. The primary resistive structures during normal respiration in the absence of adenotonsillar hypertrophy are the turbinates, with the soft palate playing a lesser role. Autonomic nervous system control of the vessels within the turbinates produces alternating engorgement and shrinkage of the turbinates, shifting nasal resistance from side to side every 1 to 5 hours. We are rarely aware of this cycling because total nasal resistance remains fairly constant. However if there is unilateral nasal obstruction from a neoplasm, polyp, or septal deviation, the total resistance will increase when the turbinates on the ‘‘good’’ side are engorged, leading to symptomatic obstruction and even mouth breathing. Such upper airway obstruction can contribute to obstructive sleep apnea, a condition with great implications for aviation safety that will be discussed in a subsequent section.

THE FOCUSED OTOLARYNGOLOGIC EXAMINATION The ability to perform a pertinent head and neck examination is essential when evaluating aerospace personnel. A detailed evaluation, including fiberoptic endoscopy, is better left to the otolaryngologist, but with a few basic aids, an adequate basic examination can be done by almost any practitioner.

Face Congenital facial abnormalities will often be immediately visible, and if they are not amenable to correction, may be disqualifying for aviation. For example, severe malocclusion, significant facial asymmetry, or a badly deformed nose can interfere with the wearing of the oxygen mask. Fortunately, most can be remedied surgically. Inspect and palpate the parotid areas, as asymptomatic tumors of the gland are fairly common and easy to miss.

Hearing Virtually anyone who is applying for aerospace training or is undergoing a required periodic physical examination should get a standard screening audiogram. If the audiogram shows significant asymmetry in thresholds between ears, or if the subject complains of a unilateral loss before getting the audiogram, a tuning fork examination may give some preliminary information until a complete audiogram can be done. The 512-Hz fork is the single most useful one to keep handy, and can help differentiate between a conductive and a sensorineural loss. The simplest test to perform is the Weber, in which the fork is struck on the heel of the hand and placed at the top of the subject’s forehead using moderate pressure. If the screening audiogram shows a 10 dB or greater difference between ears at 500 Hz, the fork will likely lateralize (be heard better in one ear than the other). As a rule, if it is heard louder in the ear with the greater loss, a conductive loss is presumed. If it is heard louder in the better ear, then a sensorineural loss is more likely. This can be clinically important information, as conductive losses can often be fixed. A conductive loss may be caused by a condition that can easily be handled in the clinic, such as a cerumen impaction, or it may require sophisticated otologic surgery, such as ossicular reconstruction or replacement. Sensorineural losses are not surgically repairable, although severe losses can benefit from placement of a cochlear implant. The Weber test is helpful, but certainly not diagnostic, so a complete audiogram should be done as soon as practicable.

Ear Congenital deformities of the pinna may be associated with external canal and middle ear anomalies as well, but they are rare. Examination of the external canal and TM is more likely to reveal pathology. Because the external canal is somewhat S-shaped and runs anterosuperiorly, the pinna should be gently pulled upward and backward to straighten the canal and allow easier access for the otoscope speculum. Choose the largest speculum that comfortably fits in the cartilaginous outer third of the canal, and brace the hand holding the otoscope against the subject’s head. This can prevent unanticipated motion by you or the subject from causing the speculum to go in deeper, making contact with the extremely sensitive and fragile skin of the bony medial two thirds of the canal. Cerumen or foreign bodies (which come in all sizes and shapes) may obscure all or part of the TM and should be removed in order to complete the examination. This may require specialty consultation. The normal TM is light gray in color and somewhat transparent. If pneumatic otoscopy is performed, the TM should move freely in and out while the bulb is squeezed and released. Do not squeeze too firmly, especially if the speculum is making a tight seal in the canal! Movement is more easily seen if the bulb is squeezed gently and rapidly. Lack of movement may indicate a hidden perforation or a middle ear effusion. Next, ask the subject to perform the Valsalva maneuver (detailed in a subsequent section), and look carefully for a slight but definite outward movement of the TM. Absence of visible movement is

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not necessarily a sign of pathology, but it does indicate the need for further evaluation, including tympanometry. Tympanometry, also known as impedance audiometry, can reveal the presence of significant negative middle ear pressure and effusion, both of which are indications of Eustachian tube dysfunction. A normal tympanogram is therefore reassuring when TM motion is not visualized during Valsalva.

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Skin Recreational and occupational sun exposures carry a real risk of skin malignancy, so examining the skin of the head, face, and neck is important. The most susceptible areas include the ears, nose, and lips. Early detection is vital, as small lesions may be easily cured. A magnifying glass can help in the examination. Specialty referral is advised for any suspicious lesion.

Nose If a head mirror or electric headlight is not available for the examination, use an otoscope with a large speculum. Look for septal deviations, markedly swollen inferior turbinates, and masses such as polyps or tumors. If the subject complains of nasal obstruction but no cause is apparent, look for inspiratory collapse of the nasal valve area just anterior to the nasal bones. If seen, ask about a history of rhinoplasty, because such collapse on normal inspiration may mean that the cartilages were weakened by surgery. Septal deviations are very common, and often cause no symptoms, so in many subjects they can be ignored. Polyps are seen as shiny yellowish or gray grape-like structures, and can range from barely visible to actually protruding from the nostrils. They usually indicate the presence of a condition that is aeromedically significant. Tumors may have ulcerations or bloody crusting. The nasal examination will be more complete if a topical decongestant is sprayed in both nostrils several minutes in advance.

Mouth and Throat Malignant lesions in this area, particularly on the floor of the mouth and in the base of tongue, can be particularly difficult to see on a cursory examination. Be sure to lift the tongue with a wooden depressor and inspect all areas carefully, especially if the subject is a smoker or a heavy drinker. Smokeless tobacco users should have the inside of the lower lip and buccal mucosa visualized. If tonsils are present, significant asymmetry is worrisome for neoplasm. Fasciculations or deviation of the tongue may indicate neurologic disease. Although not routinely done, palpation of the back of the tongue may reveal a firm or hard area that could well be a malignancy, especially in a subject that has a neck mass. Although some tumors in the oral and pharyngeal area are frankly exophytic, many are ulcerated or appear as white or red patches. Suspicious lesions must be biopsied as soon as possible. Persistent hoarseness or pain is an indication for specialty referral.

Neck Palpate the neck for masses or tenderness, paying special attention to the thyroid, lymph nodes, and submandibular salivary glands. Have the subject swallow while observing the thyroid for mobile masses (ideally with the light source shedding tangential light on the neck), then palpate the gland before and during swallowing. Many examiners prefer to stand behind the subject while palpating with both hands. Palpable or visible masses anywhere in the neck must be evaluated further. Listen for bruits over the carotid arteries.

OPERATIONALLY SIGNIFICANT DISORDERS Ear Noise-Induced Hearing Loss Progressive hearing loss due to occupational noise exposure is a widespread and serious problem, resulting in individual impairment and costing the government and industry hundreds of millions of dollars a year in compensation payments; much of it is preventable. The U.S. military services mandate enrollment in a hearing conservation program for all members who are expected to be exposed to high levels of noise during their careers. The program involves periodic audiograms, education, workplace sound level measurements, and provision of personal hearing protection. Continuous noise is more harmful than intermittent noise, and over time is more likely to impair hearing in the lower speech frequencies than is intermittent noise. Fortunately, neither type of noise causes a profound hearing loss, but they both cause early damage in the higher frequencies. Loss in these frequencies impairs speech discrimination due to muffling of consonants, and is most noticeable when there is background noise. When it is impossible to escape noise, and when engineering solutions have been maximized, hearing protection is all that is left. Those workers who are exposed to persistent loud noise, such as flight-line personnel, will usually wear double protection in the form of insert earplugs and over-the-ear muffs. Together, when worn properly, they can be fully protective during a normal working day provided ambient noise levels remain less than 125 dB, but while wearing them communication is difficult at best. Aircrew must be able to communicate in the face of high levels of noise, and when double protection is worn, maximum radio volumes may still not be adequate. Active noise reduction headsets can be quite effective at attenuating unwanted background noise, but some are bulky and all require additional electronic components. A cheaper, lighter, and equally effective solution is to use communication earplugs, which occlude the ear canal like standard soft earplugs, but they also function like music player ‘‘ear buds.’’ Radio communications bypass the occlusive effects of the earplug and allow for clear reception at comfortable volumes, while the plug itself provides background noise attenuation. Acoustic Trauma This term refers to a sudden hearing loss caused by an extremely loud noise. It is not a progressive loss as seen in

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chronic occupational noise exposure. A gun fired close to the ear or a powerful firecracker going off nearby typically causes it. There may be a small degree of hearing recovery over a few days, but most of the loss is immediate and often permanent.

Sudden Hearing Loss (Idiopathic Sudden Sensorineural Hearing Loss) This is a medical condition and is not caused by noise. It may develop over minutes or days. It is often noticed upon awakening, and about half of patients experience some dizziness or vertigo. Viral, vascular, and autoimmune causes, as well as internal inner ear membrane disruptions have been postulated and investigated without definitive answers. Patients are usually middle-aged or younger, and many recover most or all of the lost hearing within weeks. The only treatment that has yielded data showing a positive effect is an oral steroid taper at sufficient doses over 10 days (1,2). Factors working against recovery are older age, severe initial loss, vertigo, and delay in seeking treatment. As long as no underlying disqualifying condition is diagnosed, a history of sudden hearing loss should not by itself preclude aviation duties. Otitis Externa Most cases of external ear infection are acute and easily treated. Chronic cases do occur, and can be quite stubborn. The responsible microbes are more likely to be bacterial than fungal, with the common culprits being Pseudomonas aeruginosa and Staphylococcus aureus. Susceptibility is increased by warm, humid weather, water immersion (particularly, in fresh-water pools), and use of cotton-tipped applicators that can abrade the skin and remove protective cerumen. Optimal treatment includes cleaning of the infected canal, irrigation with an acidifying solution, instillation of antibiotic drops, and, if the canal is too swollen to allow drops to enter, placement of a temporary wick. During the acute phase, the ear may be too tender to wear a flight helmet or a headset, and hearing may be down due to canal occlusion. Once the infection has cleared, all flying duties can resume. Cerumen Impaction Cerumen accumulation is common, but it is almost always harmless because it rarely results in total impaction. A large collection of hard cerumen in the ear canal can cause pain by contacting the sensitive inner bony part, and may even rest against the TM. The pain can be quite noticeable when chewing, yawning, performing the Valsalva maneuver, or trying to insert an earplug. Cerumen should be removed if the TM must be seen, or if it is causing pain or hearing loss. Removal techniques are many, and with the exception of simple instillation of dilute hydrogen peroxide, all entail some risk of canal injury or TM perforation. Irrigation should not be used if there is a history of perforation, but otherwise it is fairly safe if done gently. Use only warm water, with or without peroxide. Hot or cold water can cause a nauseating caloric reaction. Softening drops may be useful in improving the results, but difficult removals should be referred.

Acute Otitis Media Acute otitis media (AOM) is common in very young children, but is almost never seen in adults, so it is not of significant day-to-day concern for the flight surgeon. It can arise during an URI, and is usually quite painful. The TM will be hypervascular or frankly reddened, may be bulging, and can even perforate with subsequent visible drainage from the hole. Proper treatment is a controversial topic, mainly because two of the common bacteria that cause AOM (Streptococcus pneumoniae and Hemophilus influenzae) are showing increasing levels of antibiotic resistance, probably as a result of overprescribing in questionable cases and undertreating in appropriate cases. In 2004, the American Academy of Family Physicians published guidelines that recommended, in selected cases of clinically diagnosed acute bacterial otitis media, that antibiotics may be withheld for 48 to 72 hours as long as close contact with the parents or patient is maintained and adequate pain relief is offered (3). A metaanalysis of 80 studies on the use of antibiotics in AOM (4) concluded that when looking at symptom relief, there is no evidence to support the use of one antibiotic regimen over another. There is also no consensus on duration of treatment, so specific recommendations on antibiotic choices and dosages will not be made here. Grounded aircrew may return to flying when the infection has clinically resolved and the Eustachian tube is functioning normally. Barotitis Media Also known as otitic barotrauma or ear block, barotitis is particularly common in aircrew trainees, but is also seen in experienced aviators who fly with colds. Pressure, typically followed by excruciating pain, begins during descent, and if the middle ear does not clear, a serohemorrhagic effusion often results. Depending on the magnitude and rate of the pressure change, the effusion may be clear to frankly bloody. Unlike in divers, TM perforations are rare in aviation personnel. Young enlisted military trainees have more problems because many of them have never experienced rapid pressure changes before and have no idea of how to equilibrate the pressure. Before their initial hypobaric chamber training, they are instructed to equilibrate by yawning, swallowing, or performing a Valsalva maneuver. Swallowing and yawning become less effective as the pressure differential between the middle ear and ambient air increases, so the trainees usually resort to the Valsalva maneuver, which is often unsuccessful even if they have physiologically normal Eustachian tubes. Failure of the Valsalva maneuver is typically due to the subject failing to transmit lung pressure to the nasopharynx where the Eustachian tube openings are. Most of the time they either have their vocal cords tightly shut or their tongue and pharyngeal muscles pushed together, effectively blocking the Eustachian tubes. The proper technique is to be sure that lung pressure is transmitted directly to the nostrils, and this can be demonstrated by releasing the nostril pinch and seeing if there is a burst of air from the nose. Once pressurized air is definitely reaching the nasopharynx and nose, then

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ventilation can happen. Practicing using the tensor veli palatini muscles by barely beginning a yawn will add to the chances of success. Deviating the chin and tilting the head away from the side that is not equalizing can also help. The use of a nasal decongestant spray may help, but often the only solution is to ascend in the aircraft (or altitude chamber) and try the maneuver at a higher altitude. Because the Eustachian tube can effectively ‘‘lock’’ when the differential pressure exceeds 80 to 100 mm Hg, ascending can reduce this differential and unlock the tube. If nothing works, it is possible to relieve the block mechanically using a pressure-generating Politzer device. These are usually available in altitude chambers, but play no role in aircraftrelated barotitis. The good news is that the ear pain rarely persists once ground level is reached, and if there is an effusion, it will usually clear in a week. The decision to ground should be based on what caused the block. A subject with an URI should be grounded until the cold symptoms and any effusion are gone and the middle ear ventilates normally. A trainee who ‘‘just got behind’’ should be grounded until the time that he or she can demonstrate an effective Valsalva. Because there is the possibility that straining while attempting a Valsalva can cause a drop in cardiac output and blood pressure lasting up to 20 seconds, and in older individuals can increase the potential for arrhythmias, the Toynbee maneuver is a safe alternative. It is performed by simply swallowing while pinching the nose and closing the mouth. When done with no pressure differential, it opens the Eustachian tube and actually causes a small amount of air to be pulled out of the middle ear. Because slight retraction of the TM results, the Toynbee is often used as a visual test of Eustachian tube patency. When a pressure differential does exist, equalization can occur in either direction during the short time the Eustachian tube is open. There is another Valsalva-like technique called the Frenzel maneuver. It is easy to perform, and is probably safer than the Valsalva, as there is no danger of generating large pressures that could perforate the TM, blow out an inner ear window, or cause hypotension. It is done by opening the jaw, filling the mouth with air, pinching the nose, pursing the lips, and then closing the jaw while displacing air posteriorly by pushing the tongue up and back. It is important to keep the vocal cords closed, and it helps to contract the ‘‘yawning’’ pharyngeal muscles at the same time. Once it is done successfully, repeating it becomes almost instinctive. Another cause of ear barotrauma is delayed barotitis or ‘‘oxygen otitis.’’ It can happen to anyone who has been breathing high concentrations of oxygen, and is due to absorption of the oxygen in the middle ear as it equilibrates with the mucosal oxygen. It can create significant negative middle ear pressures, and is prevented by early and frequent Valsalva or swallowing. If the oxygen exposure is close to bedtime, the middle ear does not get a chance to fully equilibrate, and it is possible to awaken with ear pain and even an effusion. It may be wise to set an alarm as a reminder to clear the ears during the night.

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Perilymphatic Fistula Excessive straining, sudden marked pressure changes, or ossicular displacement can rupture either the oval or round window, resulting in a perilymph leak. Perilymph is one of two chemically dissimilar inner ear fluids, and it interfaces with both the round window membrane and the stapes footplate. Symptoms include fluctuating hearing loss, vertigo, and imbalance. Once diagnosed, symptomatic treatment should be offered and the subject put at rest with the head elevated. Specialty consultation is imperative, and if symptoms do not resolve in a few days, surgical exploration could well be advised. Before considering returning the aviator to flight, symptoms must be completely resolved without any evidence of recurrence for at least 6 months; some authorities mandate that it be a year. Physical Qualification for Flight following Otologic Surgery Simple repair of an eardrum perforation with a fat or fascial graft is successful in more than 90% of cases (5), and once the surgeon states that healing is complete, which may be as little as a month after surgery, flying may resume as long as Eustachian tube function is normal. More complicated surgeries, such as removal of a cholesteatoma from the middle ear or mastoid, can take a much longer time to heal, and consideration of a waiver should be delayed until then. Postoperative evaluation of hearing and Eustachian tube function is necessary, and it would not be unusual to find that, for several reasons, the hearing in the operated ear is worse than before surgery. A hearing-loss waiver would then have to be considered once the hearing loss has stabilized. There are no data to indicate that there is value in postoperative altitude chamber testing. Surgery for otosclerosis, a disease that immobilizes the stapes footplate in the oval window, involves either fenestration of the footplate or its total or partial removal. Surgery is considered when the disease has caused a large conductive hearing loss that is problematic for the aviator. Hearing aids work well in otosclerosis because the cochlea is often normal, and all that is needed is an increase in volume. However, hearing aids can be a nuisance, and are usually unsuitable for use in the cockpit due to discomfort and sound distortion. Because volume alone can overcome the hearing loss, it would be ideal if the left-right balance of aircraft earphones could be adjusted. Unfortunately, with many systems this is not possible. During the surgery, one end of the stapes prosthesis is attached to the incus and the other end just reaches the surgical opening in the oval window, interfacing with the inner ear’s perilymph. The opening is sealed with a tissue graft. In the past, it was common to remove the entire stapes, leaving a relatively large opening in the oval window. Newer techniques involving precision laser fenestration of the footplate (stapedotomy) and the fitting of a small-diameter piston into the fenestration have reduced the risk of operative inner ear damage and postoperative perilymph fistula. As a result, the previous almost universal recommendation for a year-long grounding period has been

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modified by some agencies, and the U.S. Navy, the U.S. Air Force, and National Aeronautics and Space Administration (NASA) now consider a 3-month period sufficient as long as hearing has stabilized and there have been no episodes of vertigo or imbalance beyond the immediate postoperative period; the U.S. Army grounds its aviators for 6 months, then restricts them to dual-pilot status for another 2.5 years. There is no universal requirement for an altitude chamber test, although the U.S. Air Force does require a chamber test with rapid decompression and rapid descent, if a complete stapedectomy was done. If the newer stapedotomy technique was done, then altitude chamber exposure will not contribute anything further to a waiver decision if the subject is able to easily clear the ear on the ground without any vertiginous sensation. Surgical removal of an acoustic neuroma can affect hearing, balance, and facial nerve function. Detailed specialty consultation is necessary in order to make the best therapeutic decision among observation, surgery, and radiation. A waiver decision should be delayed for at least 6 months after treatment, and again would require specialty consultation. The U.S. military services have several cases of tactical jet aviators who have returned to the cockpit following acoustic neuroma surgery, so it is not necessarily a career-ending diagnosis.

Vertigo One of the most difficult diagnoses for a flight surgeon to evaluate is that of vertigo. In medical practice, many patients will present with a simple complaint of ‘‘dizziness.’’ When questioned further, they will variously describe the sensation as feeling ‘‘light-headed,’’ ‘‘faint,’’ ‘‘woozy,’’ or ‘‘spacey’’ and sometimes actually state that they have vertigo. This discussion will focus on true vertigo, defined as a ‘‘hallucination of motion,’’ which is commonly manifested as a spinning or tilting sensation. To an aviator, the word vertigo most often means spatial disorientation; because this is not an ENT diagnosis, it will not be discussed in this chapter (see Chapter 6). True vertigo, no matter how infrequent or brief the episodes are, carries the very real risk of an aviator losing control of the aircraft, and it must be evaluated thoroughly. Both an otolaryngologist and a neurologist should be consulted, and the subject grounded until a diagnosis is reached and the vertigo has completely resolved. Initial evaluation must begin with an extremely thorough history, as often the history provides the most vital diagnostic clues. Besides specialty consultation, further investigation may include blood chemistries, audiometry, posturography, oculography, CNS imaging such as magnetic resonance imaging (MRI) and MR angiography, electrocardiography, and even advanced vestibular tests such as vestibular evoked myogenic potentials (VEMPs). The VEMP and other advanced tests are not in common use and their utility as clinical tools and in making waiver decisions are not entirely clear. A common cause of vertigo that occurs only with head position changes is benign paroxysmal positional vertigo

(BPPV). The diagnosis is made by combining the classic history (delayed onset of spinning vertigo lasting less than a minute following a provocative head movement) with the physical examination (a crescendo–decrescendo pattern to the nystagmus and vertigo, clockwise or counterclockwise nystagmus, and a decrease in severity with repeated closeinterval testing). The underlying condition, known as canalithiasis, is thought to be caused by otoconia (the calcium carbonate crystals that normally lie on top of the hair cells in the utricle and saccule) taking up a new position in one of the semicircular canals, usually the posterior. Many cases are idiopathic, but there is an underlying ear disease or a history of head trauma in a significant number of subjects, so a more extensive evaluation may be indicated. Current treatment virtually always utilizes a canalith repositioning technique, and the Epley maneuver is most commonly used (6). The technique involves slowly and precisely moving the head and body through four positions, and when properly done for a correct diagnosis of BPPV, the immediate cure rate is approximately 90%, although recurrences are possible. If the Epley maneuver fails, it can simply be repeated. After treatment, the subject is told to refrain from lying flat, and to sleep with a few pillows under the head and torso for 48 hours. Flying may resume a week or so after treatment, providing there is no evidence of vertigo or nystagmus after performing provocative head movements. The catch-all diagnosis of labyrinthitis was once commonly made when vertigo, nausea, vomiting, and nystagmus came on rapidly. Currently, a more specific diagnosis is possible, and many of these cases are now classified as vestibular neuronitis, believed to be a viral monocranioneuropathy that involves only the vestibular portion of the eigth cranial nerve. The sudden drop in CNS input from the affected labyrinth triggers an intense perception of motion. Vestibular neuronitis, also known as vestibular neuritis, favors persons in the 30s to 40s and is self-limited, with most victims recovering completely in several weeks. There is evidence that a brief course of an oral steroid shortens the clinical course and hastens recovery of vestibular function (7). Acute symptoms should be treated with vestibular suppressants such as antihistamines (meclizine), phenothiazines (promethazine, prochlorperazine), or short-acting benzodiazepines (diazepam, clonazepam). Newer antiemetics such as ondansetron and granisetron, usually reserved for treating nausea and vomiting associated with chemotherapy, may be used when nothing else is effective. Neurologic consultation is helpful, especially when there are other cranial nerves involved. Once recovery is complete relapse is rare, so flying may be resumed at that time. M´eni`ere’s disease is an idiopathic increase in pressure of the endolymph within the inner ear. It may eventually involve both ears, but it initially presents with unilateral symptoms. A classic M´eni`ere’s attack is characterized by episodic vertigo (often of very sudden onset), fluctuating hearing loss, low frequency tinnitus, and an unpleasant sensation of ear pressure. It is generally believed that the symptoms are caused by the mixing of both endolymph and

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perilymph due to small ruptures of internal membranes within the inner ear. This admixture has an abnormal potassium concentration that is neurotoxic to the hair cells in both the cochlea and labyrinth. The history, supplemented with complete audiometric testing, will point to the diagnosis in most cases. An oral diuretic and a low-salt diet may reduce the frequency and severity of the symptoms, but surgical sectioning of the vestibular nerve is the only method of eliminating the vertiginous episodes. Surgical sectioning is not guaranteed to be effective. After nerve sectioning, the hearing loss may progress because the underlying state of increased endolymph pressure is not changed. Middle ear instillation of gentamicin has been used for years, and can be effective in reducing vertigo episodes, but can present a significant risk to hearing. A newer technique that uses a micropump to deliver the drug to the area of the round window membrane through an indwelling microcatheter appears promising, with the added benefit of causing little or no hearing loss. Waivers are seldom granted for M´eni`ere’s disease, but they may be considered when vertigo has been absent for at least a year and the subject will not be flying solo. Alternobaric vertigo is a curious phenomenon that occurs mainly in aviators when one middle ear vents positive pressure significantly faster than the other does or when a vigorous Valsalva maneuver clears only one ear. There is a sensation of true spinning vertigo that may last from seconds to a minute. It is unlikely to be reported if it is an isolated, very brief episode, but some subjects are prone to it, which makes their fitness to fly questionable. Space Motion Sickness will be covered in Chapter 6. It is not due to a pathologic condition, but rather is induced at the onset of microgravity when the otolithic organs (utricle and saccule) no longer have their usual resting one-G input. Conflicting visual cues combine to create one to several days of symptoms in most space fliers. Vestibular suppressant injections are quite effective in reducing the symptoms, and research into ground-based adaptation strategies is ongoing.

Nose and Sinuses Trauma Sinus fractures seldom occur except in heavy blows to the face such as seen in traffic collisions. Most facial fractures can be repaired surgically, and sinus function is not likely to be affected. Nasal fractures on the other hand are quite common, and a visible deformity should be reduced by an otolaryngologist. It is extremely important to examine the inside of the nose for a septal hematoma whenever it has sustained a blow of sufficient force to cause bleeding. Hematomas obstruct both nares, and may occur even when the external nose has not been deformed. Untreated, they can lead to necrosis of the cartilaginous septum with an eventual ‘‘saddle’’ deformity of the nasal dorsum. A simple septal deviation without symptoms does not need to be straightened, and even those causing mild symptoms can be ignored if sinus ostial blockage is not present.

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Septal perforation is a known complication of septal surgery, and if it is not causing recurrent bleeding or whistling during respiration, it does not need to be repaired. In fact, larger perforations are quite difficult to repair, so if there is no bleeding or whistling, it may be best to leave them untreated. If there are symptoms, a silicone button can be inserted to block the perforation. A perforation without a prior history of trauma or surgery should be investigated further because of the possibility that it is secondary to granulomatous disease, neoplasm, or even cocaine abuse. Benign septal perforations without recurrent bleeding should not bar the subject from flying.

Intranasal Disorders It has been estimated that one fourth of the population have allergic rhinitis at some time during the year. Symptoms may be seasonal due to pollen exposure or perennial due to dust mite exposure. Diagnosis is straightforward when symptoms of rhinorrhea, sneezing, lacrimation, and nasal itching coincide with a particular pollen season. Less obvious cases will need to be evaluated by an allergist. Treatment can include nasal saline rinses (8), oral nonsedating antihistamines, topical nasal steroid sprays, leukotriene modifiers, and allergy immunotherapy (injections). Immunotherapy is reserved for severe or refractory cases, mainly because it must be continued for 3 to 5 years. In addition, because of the possibility of a reaction, they should only be given in a practitioner’s office. All of these treatments are compatible with flying if they are effective and have no associated side effects. Acute rhinosinusitis is typically a self-limited viral infection. During the infection, the risk of ear and sinus barotrauma is greatly increased, so grounding should continue until all symptoms have resolved. Symptomatic medications may be used, but antibiotics should be avoided unless there is evidence that the infection has become bacterial. Persistent unilateral purulent drainage, coupled with ongoing pain localized to a sinus on the same side, would be adequate evidence. Antibiotic therapy follows established guidelines (9). Flying should not resume until signs and symptoms have resolved, but if flying as a passenger is unavoidable before complete recovery, use of a topical nasal decongestant spray such as oxymetazoline is recommended to reduce the chance of sinus and ear barotrauma. Topical nasal steroids can also help in reducing nasal mucosal edema, but are slow to act and are not useful in acute situations. The practitioner should check Eustachian tube function off decongestants before returning the subject to flying duty. Chronic rhinosinusitis is a symptomatic condition that lasts more than 3 months. It is a bacterial infection that often shows less severe signs and symptoms than acute rhinosinusitis, and aviators commonly try to fly in spite of them. Sinus barotrauma may be the first indication that a problem exists. Diagnosis requires not just a careful history and ENT examination, but a coronal CT scan as well. Initial treatment with long-term antibiotics is worth trying, but many of the subjects whose flying careers are

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on hold will eventually undergofunctional endoscopic sinus surgery (FESS). The surgery has a high initial return-to-flying rate, although recurrences can and do happen, so periodic reevaluation is always advised. Ideally, all postoperative subjects should undergo a functional test in a low-pressure chamber before being considered for return to flight. There is no need to go to an altitude higher than 18,000 ft, so the risk of decompression sickness during the test is minimal. Although nasal polyps may be a manifestation of allergic rhinitis, they are equally likely to be caused by chronic infection or, less commonly, conditions such as aspirin sensitivity and cystic fibrosis. Not only can polyps cause annoying nasal obstruction, they are also likely to cause sinus barotrauma. Smaller polyps may shrink with topical nasal steroids and/or a short burst of systemic steroids, but the larger ones are best treated surgically. When polyps are seen, a coronal sinus CT is indicated because it will often show evidence of widespread sinus mucosal thickening. For this reason, endoscopic sinus surgery is usually necessary to remove areas of infection and diseased mucosa in addition to the polyps. If not removed, this mucosa will continue to hinder sinus aeration and lead to more infection and polyp formation. The decision on when to return the subject to flying, as well as the postoperative recommendations, are the same as for chronic rhinosinusitis. Solitary unilateral polyps in an otherwise normal individual should be evaluated as possible neoplasms. Chronic nasal congestion that has no underlying allergy, infection, or intranasal mass may be due to vasomotor rhinitis. Sensitive nasal mucosa and reactive turbinates may swell at seemingly minor provocations such as temperature and humidity changes, assorted odors, nasal irritants, recumbency, and even emotional swings. Thin, clear rhinorrhea can be present as well. Topical nasal steroid sprays can help, but the symptoms can be surprisingly resistant to any treatment. A possible etiology is instability of autonomic control of the nasal vasculature. Grounding is not necessary unless there are functional problems with altitude exposure. Rebound nasal congestion is seen in subjects who overuse nasal decongestant sprays. The worsening congestion leads to more frequent use of the medication, and eventually it becomes refractory to virtually any amount of spray, yet it continues to be used. Weaning from the decongestant is necessary, and can be aided by the use of oral decongestants, topical steroid sprays, and saline irrigations or mists. If progress is slow, a short course of an oral steroid may be added. It may be necessary to ground the aviator during the weaning period because of signs of decongestant ‘‘withdrawal’’ that can include significant emotional distress.

Sinus Barotrauma Sinus barotrauma, also known as barosinusitis or sinus block, is most common in persons who fly with a URI, but as mentioned earlier, it can also be an indicator of chronic sinus problems. A sinus block in an experienced aviator who has no acute cold symptoms is an indication for further investigation. The injury is caused by increasing

negative pressure within the affected sinus during descent. This relative vacuum causes rapid mucosal congestion, often with formation of a submucosal hematoma that result in extremely sharp and intensely distracting pain of sudden onset. For this reason alone it represents a hazard to safe flight. Isolated barosinusitis that happens in the course of a URI does not need an in-depth evaluation, so flying can resume once the cold symptoms are gone. In contrast, recurrent barosinusitis, even in the presence of obvious cold symptoms, should always be investigated further. The frequency of finding underlying pathology is surprisingly high.

Flight Qualification following Nasal and Sinus Surgery It is fortunate that most nasal and sinus surgery leads to a resumption of flying, but follow-up, specifically after sinus surgery, should continue for the length of a flying career, if not lifelong. Recurrence of chronic sinusitis and polyps will lead the flyer back into familiar signs and symptoms, with the renewed risk of sinus barotrauma. Regular checkups, as frequently as every 4 to 6 months, can spot a recurrence when it is easiest to treat and when it has less chance of causing a lengthy period of grounding. Waiver recommendations should always include appropriate follow-up intervals, and if they are faithfully adhered to, there is relatively little chance of a major career interruption.

Oral Cavity, Pharynx, and Neck Oral Cavity Conditions The vermilion of the lower lip and the vermilion-skin border of the upper lip are prone to develop squamous cell carcinoma due to sun exposure. Because of their prominent location, most should be diagnosed early, and local excision can often be curative. Healing after treatment is rapid, and there should be only a short period of grounding, with regularly scheduled reexaminations to look for recurrences or new lesions. If the cancer has already metastasized to regional or distant lymphatics, treatment will be much more extensive, and a decision to return the subject to flying will depend on factors best evaluated by appropriate specialists. Recurrent herpes simplex lesions commonly erupt in the area around the vermilion-skin border and are self-limited, but an initial oral herpes infection can cause a widespread mucosal outbreak that would be cause for grounding. In both cases the lesions are transmissible, so hand or mouth contact with others is unwise during the symptomatic phase. Early treatment with oral antivirals may shorten or even arrest the outbreak, and antiviral ointments can be of some help in lip lesions. Aphthous ulcers (canker sores) can be painful out of proportion to the small area they cover. Typically, they heal within 2 weeks, but some unfortunate patients seem to produce new lesions before the old ones have healed. The etiology is uncertain and the list of suggested precipitating factors is long, including stress, oral trauma, cessation of smoking, and progesterone level fluctuations during the

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menstrual cycle. However, supporting evidence is scarce (10). The ulcers are small, with a yellow or gray base and a reddened border. Treatment is symptomatic, and triamcinolone in a carboxymethylcellulose paste is popular and relatively effective. Tetracycline and chlorhexidine gluconate mouth rinses also show evidence of efficacy. If pain is prominent, 20% benzocaine in carboxymethylcellulose paste can give immediate relief. Although they may assist healing, none of these preparations will prevent the next outbreak. Fortunately, grounding is rarely necessary. Large, multiple, frequent, or persistent ulcers (>3 weeks) require a more in-depth evaluation for possible underlying illnesses.

Pharyngeal Conditions Acute pharyngitis is common during many colds, and leads to reddened mucosa, often with tender cervical lymph nodes. Most infections are viral, but if fever, malaise, and mucosal exudates are present, there is a chance that the infection is bacterial and a rapid streptococcus screen should be done. A positive screen test result for Group A β-hemolytic streptococcus indicates the need for antibiotics, but antibiotics may also be indicated when the result is negative if there is high fever, marked malaise, or necroticappearing tonsils. Infectious mononucleosis due to the Epstein-Barr virus (EBV) can present as severe pharyngitis and tonsillitis with prominent cervical adenopathy. Elevated heterophile antibody titers as evidenced by a positive Monospot test, and a complete blood count that shows an abnormal number of atypical lymphocytes, help confirm the diagnosis (although the Monospot test may not become positive early in the course of the disease). More expensive EBV-specific antigen and antibody tests may be useful in determining if the infection is recent or occurred previously, but are usually not necessary. Mononucleosis is a systemic illness, with liver and spleen involvement that can cause enlargement of both organs. Liver function tests should be done, and the individual should not participate in contact sports until recovery because of the danger of splenic injury. Steroids with and without antivirals have been used in the treatment of severe symptoms, but have not been shown to be of significant benefit (11–13). Because in some cases malaise and fatigue can be prolonged, flying should be avoided until all symptoms and signs (including hepatosplenomegaly) are gone. Cervical lymph nodes may be slow to return to baseline, and if all other manifestations of mononucleosis have resolved, flying can resume. Acute tonsillitis is often part of the usual URI-related acute pharyngitis, but occasionally the pain in one tonsil will rapidly increase, with difficulty swallowing, trismus, and voice change (the so-called hot potato voice that results from the victim trying to avoid painful tongue movements). These are the classic signs of a peritonsillar abscess, and treatment is aimed initially at draining pus from the abscess cavity. Aspiration of the cavity with a no. 18 needle can be very effective, and should be supplemented by antibiotic treatment, pain relief, and rehydration. If pus reaccumulates,

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the abscess cavity might require wide incision and drainage. Tonsillectomy may be done acutely in this setting. Whether a tonsillectomy should eventually be done is debatable, but in cases of recurrent tonsillitis and/or recurrent abscesses, it may be recommended. Once symptoms have resolved, the subject can return to flying. Snoring is often regarded as a simple social problem, but bad snorers may be headed for a more serious condition known as obstructive sleep apnea syndrome (OSAS). Sleep apnea is seriously under-recognized, and there is frequently a long delay in diagnosis, especially in persons who sleep alone. The cardinal symptom, and the most worrisome one in anyone who drives or flies, is excessive daytime sleepiness. This is the result of fragmented and nonrefreshing sleep that comes from frequent arousals due to an intermittently obstructed upper airway. Associated symptoms are morning headache, dry mouth and throat, fatigue, irritability, and difficulty with concentration. Sufferers may gasp, snore, and have both audible and visible obstructive apneic episodes. Men are approximately twice as likely as women to have the condition, but men outnumber women by as much as 8:1 in sleep center referrals, possibly because of reluctance by women to acknowledge that they have a snoring problem. Risk factors include obstructing lesions of the upper airway, obesity [body mass index (BMI) >30], neck size greater than 17 in. regardless of BMI, older age, retrognathism, a visibly elevated tongue base, a narrowed oropharyngeal airway, and alcohol use. Any or all of these factors can contribute to obstruction of the airway, often with dramatic drops in arterial oxygen saturation. A thorough head and neck examination along with an in-depth history (and an interview with the bed partner) should be done before referring the subject to a sleep center. If untreated, OSAS can contribute to metabolic syndrome, and is known to increase the incidence of myocardial infarction, stroke, and sudden nighttime death. In the driving and flying population, mishaps from falling asleep at the controls are a real possibility. Once OSAS is diagnosed, the primary treatment is to administer continuous positive airway pressure (CPAP) during sleep using a nasal appliance. When it is used for 6 or more hours a night, it can completely reverse all symptoms and even improve the insulin resistance seen in metabolic syndrome. If CPAP is rejected for any reason, surgery, including uvulopalatopharyngoplasty (UPPP), maxillary and mandibular advancements, and tongue reduction may help, although CPAP has by far the better record of success. In rare cases, the only effective treatment is tracheostomy, which completely bypasses the obstruction but is incompatible with flying. Aviation personnel with known or suspected obstructive sleep apnea must be grounded and referred for objective evaluation, which should include polysomnography performed at a sleep center. If OSAS is diagnosed, it must be treated. If applicable, treatment should include weight loss. A return to flying should only be considered if posttreatment interviews combined with a new sleep study show that the condition has been eliminated and the patient successfully passes a maintenance of wakefulness

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test. There is a temptation for some subjects on CPAP to let the treatments lapse, and within days to weeks they have a return of all symptoms, so it is important to keep in close contact with them. Fortunately, most people find that CPAP makes them feel so much better that they never give a thought to quitting. Gastroesophageal reflux disease (GERD) can have manifestations outside the esophagus such as morning hoarseness, nagging cough, sore throat, Eustachian tube, and middle ear inflammation, and even tooth enamel erosion. When it is suspected, conservative measures are initially recommended such as eating smaller meals, avoiding evening alcohol, not eating within 3 hours of bedtime, and elevating the head of the bed. These measures may be combined with oral histamine H2 receptor antagonists. Be aware that the individual may already be taking them without the practitioner’s knowledge, as they have long been available without a prescription. Proton pump inhibitors have more recently become available without a prescription, and they are not recommended for use beyond 14 days without physician oversight. In some cases, surgery such as fundoplication may be recommended, but the effectiveness of surgery when antacid therapy has failed had not been conclusively demonstrated (14). The decision to allow or restrict flying depends on the severity of symptoms, and whether or not treatment is effective. Hoarseness of acute onset is associated with viral URIs and vocal abuse. If the onset is insidious and the hoarseness is persistent, consider GERD, vocal cord lesions, and chronic smoking-induced laryngitis. Relative voice rest should be tried for a few days, but if hoarseness continues beyond 3 or 4 weeks, the larynx must be visualized by mirror or endoscope. Most benign vocal cord lesions such as polyps, nodules, edema, and hyperkeratosis can be observed or treated surgically. Nodules may regress with intensive speech therapy, and edema may resolve after stopping smoking. Lesions suspicious for carcinoma should be biopsied. Fortunately, most malignant laryngeal lesions cause voice changes early in their course, so there is often little delay in diagnosis and treatment. The cure rates for early excisional surgery of small invasive lesions and laser therapy for carcinoma in situ are approximately 90% to 95%. Because micro- or minimally-invasive laryngeal carcinomas have such a high cure rate and so few surgical complications, once the voice has regained volume and intelligibility a return to flying is appropriate as long as regular follow-up visits are prescribed. Military policies vary; the U.S. Navy requires a 1-year grounding period after treatment of localized laryngeal cancers, but the U.S. Air Force does not specify a grounding period, only requiring that the patient be disease-free and fully recovered before a waiver can be considered. Any neck mass is a cause for concern. Although most are benign and related to nearby inflammation or infection, they all deserve close scrutiny, as many head and neck malignancies first manifest as metastatic lymphadenopathy. Evaluation should start with an otolaryngology consultation, which will usually include upper aerodigestive endoscopy, CT or MRI, and a fine-needle aspiration biopsy (FNAB)

of the mass. Incisional (partial) biopsy is rarely indicated because of the chance of causing local spread by breaching a malignant lesion. Total excisional biopsy has less chance of local seeding with malignant cells, and may be necessary if the nature of the mass remains uncertain. The removal of a proven benign mass, such as a thyroglossal duct cyst, is essentially elective if there are no troubling symptoms. Lower midline masses are likely to be in the thyroid. Thyroid masses have a malignancy rate of approximately 20%, and an FNAB may not be helpful in making that distinction. Total lobectomy on the involved side is considered standard treatment when the diagnosis is uncertain. Further surgery might be necessary in the case of a malignancy. Radioactive iodine may be used to ablate residual gland tissue and make postoperative nuclear medicine imaging more sensitive in detecting residual thyroid tissue. Thyroid hormone replacement therapy carries little risk and is compatible with flying. Malignant diagnoses require regular monitoring for growth of residual tumor or metastases, but only the most aggressive malignancies, such as anaplastic and medullary carcinomas, have poor prognoses, with anaplastic being the most lethal as most patients succumb within a few months of diagnosis. Important complications of thyroid surgery are two: vocal cord paralysis and hypoparathyroidism. Vocal cord paralysis does not always cause a significant change in voice, but it does cause difficulty in raising volume, and the airway may be slightly compromised during exercise. If the voice is excessively breathy, thyroplastic surgery can help. Unilateral paralysis would likely have no effect on flying and should not be grounding if vocal communication remains good. Bilateral vocal cord paralysis can cause immediate dyspnea upon extubation, and needs urgent treatment. Even minimally symptomatic hypoparathyroidism may never improve and can be incompatible with flying. Parathyroid adenomas rarely present as neck masses, and are only suspected when the serum calcium is elevated. Confirmatory testing reveals an elevated ionized calcium and inappropriately high parathormone (PTH) levels. Localizing an adenoma by noninvasive imaging, most commonly using a radioactive trace technique, can be difficult. Surgical options range from bilateral open neck explorations to minimally invasive techniques. If the adenoma is located and successfully removed, and PTH levels stabilize at normal levels, flying does not need to be restricted.

SUMMARY The realm of otolaryngology encompasses a number of systems and organs that must be healthy before we can undertake or continue a flying career. For instance, when the inner ear is functioning normally, we are not at all aware of its presence, but if it should malfunction, it can produce immediate and incapacitating symptoms. The same applies to the middle ear and sinuses. When normal ventilation of these structures is compromised, pain can rapidly ensue, and

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if it is not totally incapacitating, it can surely distract the aviator from the task of flying. Awareness of the pathologic processes that affect the ENT area is vital to the practice of aerospace medicine.

ACKNOWLEDGMENT The principal author of this chapter in the third edition, G. Richard Holt, MD, provided an excellent framework for the fourth edition chapter. He was unable to participate in the current edition in large part because of obligations to the U.S. Air Force Reserve, which included an extended tour in the Middle East. He has my heartfelt thanks for both his contributions and his service.

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9. Benninger MS. Therapeutic choices in the treatment of acute community-acquired bacterial rhinosinusitis. Am J Rhinol 2006;20: 662–666. 10. Scully C. Aphthous ulceration. N Engl J Med 2006;355:165–172. 11. Brandfonbrener A, Epstein A, Wu S, et al. Corticosteroid therapy in Epstein-Barr virus infection. Effect on lymphocyte class, subset, and response to early antigen. Arch Intern Med 1986;146:337–339. 12. Candy B, Hotopf M. Steroids for symptom control in infectious mononucleosis. Cochrane Database Syst Rev 2006;3:CD004402. 13. Tynell E, Aurelius E, Brandell A, et al. Acyclovir and prednisolone treatment of acute infectious mononucleosis: a multicenter, doubleblind, placebo-controlled study. J Infect Dis 1966;174:324–331. 14. DeVault KR, Castell DO. Updated guidelines for the diagnosis and treatment of gastroesophageal reflux disease. Am J Gastroenterol 2005;100:190–200.

RECOMMENDED READINGS REFERENCES 1. Chen CY, Halpin C, Rauch SD. Oral steroid treatment of sudden sensorineural hearing loss: a ten year retrospective analysis. Otol Neurotol 2003;24:728–733. 2. Wilson WR, Byl FM, Laird N. The efficacy of steroids in the treatment of idiopathic sudden hearing loss. Arch Otolaryngol 1980;106:772–776. 3. Lieberthal AS, Ganiats TG, Cox EO, et al. American Academy of Pediatrics, American Academy of Family Physicians. Subcommittee on Management of Acute Otitis Media Clinical practice guideline. Diagnosis and management of acute otitis media. Pediatrics 2004;113:1451–1465. 4. Takata GS, Chan LS, Shekelle P, et al. Evidence assessment of management of acute otitis media: I. The role of antibiotics in treatment of uncomplicated acute otitis media. Pediatrics 2001;108:239–247. 5. Aggarwal R, Saeed SR, Green KJM. Myringoplasty. J Laryngol Otol 2006;120:429–432. ¨ uo˘glu LN, Ergin NT. The canalith repositioning 6. Dal T, Ozl¨ maneuver in patients with benign positional vertigo. Eur Arch Otorhinolaryngol 2000;257:133–136. 7. Strupp M, Zingler VC, Arbusow V, et al. Methylprednisolone, valacyclovir, or the combination for vestibular neuritis. N Engl J Med 2004;351:354–361. 8. Tomooka LT, Murphy C, Davidson TM. Clinical study and literature review of nasal irrigation. Laryngoscope 2000;111:1867–1869.

Bailey BJ, Johnson JT, Newlands SD, eds. Head and neck surgery–otolaryngology, 4th ed. Philadelphia: Lippincott Williams & Wilkins, 2006. Brook I. Sinusitis. New York: Taylor & Francis, 2006. Cummings CW, Haughey BH, Thomas JR, et al., eds. Cummings otolaryngology, 4th ed. Philadelphia: Elsevier Science, Mosby, 2005. Jahn AF, Santos-Sacchi J. Physiology of the ear. New Haven: Singular, 2001. Lee KJ. Essential otolaryngology, 8th ed. New York: McGraw-Hill, 2002. Sataloff RT, Sataloff J. Hearing loss, 4th ed. New York: Taylor & Francis, 2005. Snow JB, Ballenger JJ, eds. Ballenger’s otorhinolaryngology: head and neck surgery, 16th ed. Lewiston: BC Decker, 2003.

Additional Reference Material The American Society of Aerospace Medicine Specialists has made its Aerospace Medicine Practice Guidelines available at: http://www/asams.org/guidelines.htm Pertinent to this chapter are the guidelines for Acoustic Neuroma, Allergic Rhinitis, Cholesteatoma, Gastroesophageal Reflux Disease, M´eni`ere’s Disease, Sinusitis, and Sleep Disorders. Other sources of information are the US Navy Aeromedical Reference and Waiver Guide (http://www.nomi.med.navy.mil/NAMI/WaiverGuideTopics/index .htm), the US Air Force Waiver Guide (www.airforcemedicine.afms. mil/waiverguide), and the US Army’s Aeromedical Policy Letters. https://aamaweb.usaama.rucker.amedd.army.mil/AAMAWeb/ policyltrs/Army APL

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Aerospace Neurology John D. Hastings

Listen to your patients. Listen and they will tell you what’s wrong with them. And if you listen long enough, they will even tell you what will make them well. —Walter C. Alvarez

A doctor who cannot take a good history and a patient who cannot give one are in danger of giving and receiving bad treatment. —Author Unknown

The greatest mistake in the treatment of diseases is that there are physicians for the body and physicians for the soul, although the two cannot be separated. —Plato

In the practice of medicine, the neurologist is called upon to answer the following questions (1): 1. 2. 3. 4.

Does the patient have neurologic disease? If so, what is the localization of the lesion or lesions? What is the pathophysiology of the process? What is the preliminary differential diagnosis?

Utilizing the tools of the neurologic and medical history, the neurologic examination, ancillary studies, and one’s education, training, and experience the neurologist arrives at a diagnosis. The aerospace medicine physician (evaluator) has the additional challenge of relating the neurologic condition to aviation safety and achieving an appropriate aeromedical disposition. Whether it is aviation medical examiner, flight surgeon, or regulator, the aerospace medicine physician shoulders the responsibility of a determination that may decide one’s career in aviation or space. Considering the individual, and yet preserving

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aviation safety, is a never-ending challenge for the aerospace medicine physician. The evaluator has the dual responsibility of applying the standards, and also considering exceptions to the standards in allowing waivers from standards, while assuring aviation safety. An important consideration in aeromedical disposition is the nature of the operation or the mission, as a condition might not be compromising in all aerospace operations. The evaluator must consider the condition in relation to space operations, potentially of long duration, military versus civil operations, single versus multicrew operations, and the nature of the operation. Demands within civil, private, commercial, and airline transport operations must be considered. For example, a history of migraine with certain characteristics might potentially compromise military operations where immediate worldwide deployment is possible, but the condition might be considered an acceptable risk for multicrew or private pilot operations.

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PRINCIPLES OF AEROSPACE NEUROLOGY When a neurologic condition exists, the evaluator should consider the following: 1. Is the condition static? If so, what is the degree of functional incapacitation? 2. Is the condition progressive? If so, is the course predictable or unpredictable? 3. Can the condition be monitored successfully? 4. Can the condition result in sudden incapacitation? 5. Can the condition result in subtle incapacitation? A pitfall in aeromedical disposition of aviators with neurologic disorders is making a major decision based on limited information. In neurologic diagnosis, the history is most often the richest source of information. The neurologic examination is often normal. Ancillary studies including laboratory studies, neuroimaging procedures, and sometimes sophisticated studies such as cardiac electrophysiological studies may also be normal. Often, the history is the sole means of diagnosis. One need only consider the migraineur, the epileptic with a normal electroencephalogram (EEG), the person with a transient ischemic attack (TIA) and no vascular bruit, or the victim of transient global amnesia (TGA) to grasp the importance of history. The aerospace medicine physician is somewhat disadvantaged because evaluation is based on obtained medical records and history taken by others. Most often, the evaluator has no opportunity to interact with the individual or obtain one’s own history. Yet efforts to obtain additional information when the history is inadequate often bear the most fruit. Observations of emergency services personnel, description of an event by a spouse or other observer, or comments from fellow aircrew may hold the key to diagnosis and appropriate aeromedical disposition. Diligent pursuit of a complete history is the evaluator’s best guide to aeromedical disposition. Another important consideration in neurologic diagnosis is the role of psychological factors. Symptoms that reflect true neurologic illnesses are often intertwined with complaints that have an emotional basis, and teasing out the respective contributions is important for the evaluator. Moreover, psychological influences often play an important role in a number of common disorders encountered by the neurologist. The influence of emotions in migraine, syncope, and chronic daily headache exemplifies this relationship. This chapter does not address individuals in whom neurologic disease is absent. Rather, it addresses those who suffer from a neurologic condition, which may or may not compromise aviation safety, resulting in temporary or permanent disqualification or operational limitations. The following pages will attempt to apply these principles to specific neurologic conditions encountered in aerospace medical certification.

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EPISODIC DISORDERS Episodic neurologic disorders, including migraine, cluster headache, TGA, syncope, epilepsy, the single seizure, and vertigo, are of aeromedical significance because of the potential for sudden incapacitation. Some merit permanent disqualification, whereas others may be accommodated with treatment or operational limitations. Vertigo will be dealt with in Chapter 15. Although ‘‘central’’ vertigo may occur in association with brain stem disease [e.g., multiple sclerosis (MS) or ischemic vascular disease], most cases of paroxysmal vertigo represent peripheral vestibulopathies.

Migraine Migraine is common, with a prevalence of 17% in women and 6% in men. Common features of migraine include unilaterality (exclusively or predominantly one-sided), throbbing nature, nausea, vomiting, photophobia, phonophobia, and prostration. The migraine sufferer commonly prefers a dark, quiet room and relief may follow sleep. The headache may last hours to days and is commonly followed by a drained feeling and remnants of pain with head movement. Although migraine may be spontaneous, there are many precipitants including sleep deprivation, hunger, sun exposure, fatigue, menses or oral contraceptives, foodstuffs, alcohol, and emotional stress. Migraineurs tend to have perfectionistic and orderly personality traits, and family history is positive in 60% of cases. Migraine can appear at any age but commonly in adolescence, sometimes entering remission and appearing years later. In common migraine, the headache begins without an antecedent aura. In classic migraine, an aura precedes the headache by 15 to 30 minutes. Visual auras are common with myriad descriptions including scintillating or sparkling lights, visual field defects such as hemianopia, colored or kaleidoscopic whorls or patterns, or patterns such as zigzag lightning or herringbone patterns. An important diagnostic feature is the ‘‘positive’’ nature of the visual aura, meaning the presence rather than the absence of light (ischemia characteristically is a ‘‘negative’’ visual phenomenon with absence of light). Nonvisual auras also occur, with symptoms such as marching face and hand numbness, or expressive speech difficulty. A third variety of migraine is ‘‘migraine equivalent’’ (migraine variant, acephalgic migraine), in which a migraine aura occurs without developing a headache. Visual migraine equivalents are not uncommon beyond age 40(2), sometimes being mistaken for TIA due to cerebrovascular disease. Rare forms of migraine include ‘‘complicated migraine,’’ such as hemiplegic migraine accompanied by stroke, ophthalmoplegic migraine with oculomotor nerve palsy, and basilar migraine with ataxia and confusion. Migraine may or may not be of aeromedical significance depending on its characteristics in a specific individual, and operational considerations (e.g., potential global military

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deployment versus private pilot operations). To guide aeromedical disposition, the evaluator should consider a host of factors, including the following: 1. Prodrome: Some migraine sufferers will experience a prodrome of hours to a day or more, characterized by a sense of uneasiness, anxiety, apprehension, or general feeling of ill being. Recognition of prodrome may allow the aviator to avoid flying. 2. Precipitating factors: Many migraineurs will report specific precipitating factors, which, if avoided, may reduce migraine risk or preclude migraine altogether. These include emotional stress, multitask overload, sleep deprivation, fasting, foodstuffs and certain alcohols, menses, and other precipitants. 3. Migraine aura: Is the aura minor, or is there significant functional impairment? For example, slight perioral and unilateral fingertip paresthesiae may be inconsequential, as would a sliver of shimmery light in the far periphery of the visual field. Alternatively, a complete homonymous hemianopia or prominent aphasia would significantly compromise the individual. 4. Rapidity of onset: Some migraines develop rapidly, with vomiting and prostration occurring within 15 to 30 minutes of onset. Others develop slowly, perhaps beginning as an annoying discomfort over one eye, but not developing into a severe headache for hours. Onset during flight would allow corrective measures in this circumstance. 5. Frequency: Migraine-free intervals can vary widely from days to years or even decades. An individual experiencing several migraines per month would cause concern; a frequency of two per year would be far less worrisome. 6. Acute treatment measures: Aspirin, nonsteroidal antiinflammatory drugs (NSAIDs), and acetaminophen may be effective if taken early. These would be acceptable in an aviation environment. Triptans may be acceptable with timing limitations in relation to flight. Anticonvulsants, narcotic analgesics, and barbiturate-containing analgesics would be prohibitive. 7. Preventive treatment: Medications employed in migraine prophylaxis include β-blockers, calcium channel blockers, anticonvulsants, and antidepressants including tricyclic and selective serotonin reuptake inhibiting agents. β-Blockers and calcium channel blockers may be acceptable in aviation, whereas the others are prohibitive due to potential central nervous system effects. Considering the prevalence of migraine, the diagnosis need not be disqualifying in most individuals. Individual consideration with attention to the features enumerated earlier may allow favorable aeromedical disposition depending on the aviation environment.

Cluster Headache True cluster headache, formerly known as histamine headache or Horton’s headache, has very distinct clinical characteristics. The term cluster refers to a series of headaches lasting from weeks to months separated by symptom-free intervals

of many months to several years or more. Each headache is identical for that individual. Clinical characteristics may include abrupt onset with intense pain peaking within a minute or two, unilateral location in or behind one eye, unilateral nasal stuffiness, drainage, eye redness, tearing, and perhaps a Horner syndrome (ptosis and pupillary constriction). Excruciating pain persists for 30 to 45 minutes followed by rapid resolution of symptoms. Headaches may occur precisely at the same time each day. After one or more headaches daily for a period, the cluster ends, affording welcome relief. Cluster headache is treated with narcotic analgesics and other analgesics, lithium carbonate, and at times oxygen (a potent vasoconstrictor). Severe pain and analgesic requirements during a cluster are disqualifying, but long periods of remission usually allow certification once the cluster ends.

Other Headache Although not included in the episodic disorders, the most commonly occurring headache is chronic daily headache, formerly referred to as tension headache. This is a frequent (daily or nearly so) headache, often dull to moderate, nagging but not incapacitating, with resistance to treatment. It may be a component of a somatoform disorder, and in one study 46% of individuals with a primary complaint of chronic headache suffered from endogenous depression (3). The underlying condition and therapeutic agents utilized (narcotic- or barbiturate-containing analgesics, antidepressants, tranquilizers) ordinarily preclude aeromedical certification unless underlying issues are resolved.

Transient Global Amnesia TGA is a fascinating condition whose prime characteristic is severe anterograde and extensive retrograde amnesia. Initially described in 1954, TGA is a global amnesic state that resolves within 24 hours. Personal identity, level of consciousness, awareness, and ability to perform complex acts are well preserved, distinguishing TGA from confusional states. Strict diagnostic criteria include presence of a capable witness, clear anterograde amnesia, alert wakefulness, normal content of consciousness beyond memory, absence of focal symptoms and a normal neurologic examination, and resolution within 24 hours. Although TGA has been reported from age 5 to 92 years, 90% of cases occur in the 50 to 80 range. Most attacks are 4 to 6 hours in duration, with retrograde amnesia ranging from hours to months and sometimes years, which upon recovery shrinks to a permanent retrograde gap of 1 hour. Precipitating circumstances reported in TGA include cold water immersion, sexual intercourse, painful experiences, and medical procedures such as angiography on rare occasions. Association with physical exertion is present in 18%, emotional stress in 14% to 44%, and with migraine in 25% to 33% of cases. At the onset of TGA there is disorientation for time and place, but preservation of personal identity. Repetitive asking of questions is a near universal feature. Preserved ability to perform complex acts such as operating an aircraft

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or performing detailed carpenter work is a constant feature of TGA. Migraine-like headaches are associated with TGA in approximately 50% of patients. Unilateral or bilateral medial temporal hypoperfusion has been demonstrated during TGA with magnetic resonance imaging (MRI) techniques, and experimentally, a slowly spreading cortical depression across the cerebral cortex has been shown. Interestingly, a similar mechanism of cortical spreading depression has been postulated in the aura of migraine. Most individuals with TGA suffer a single episode, although recurrence rates of 3% annually over 5 years have been reported. Aeromedical disposition often depends on specific precipitating factors and often a period of symptomfree observation. A monograph by Hodges (4) provides a comprehensive review and discussion of TGA.

Syncope The importance of history in neurologic diagnosis is clearly apparent when dealing with disorders of consciousness. Differentiating syncope from seizure (faint from fit) is a never-ending challenge for the aeromedical physician. An erroneous diagnosis has profound implications for the aviator. Up to one third of persons suffering syncope with convulsive accompaniments are incorrectly given a diagnosis of epilepsy. The essence of syncope is loss of consciousness and postural tone due to global cerebral hypoperfusion followed by spontaneous recovery. In near syncope (presyncope), the process is incomplete (perhaps by a compensatory action such as sitting down), with partial preservation of consciousness. Syncope is common, with a reported occurrence of 3+% in the Framingham Study. Approximately 75% of these individuals reported a single occurrence with a mean followup of 26 years. In a study of 3,000 healthy United States Air Force (USAF) personnel averaging 29 years of age, 2.7% reported syncope (5). In the 1942 text Fit to Fly, A Medical Handbook for Fliers, coauthored by Grow and Armstrong, the following text appears: ‘‘Low blood pressure occurs in 2.5% to 5% of the population and is probably more common in hot climates. Usually it indicates a person who is under par physically. They are usually underweight, show narrow, flat chests with poor expansion, and they commonly complain of lassitude, giddiness, vertigo, and a tendency to faint’’ (6). There are no other references to syncope in the text. Syncope occurs due to impaired homeostasis, the normal state of appropriate balance and regulation of cardiac output, circulating blood volume, and peripheral resistance provided by peripheral arterial smooth muscle. When one stands, 70% of circulating blood volume lies at or below the heart. Gravity pools 500 to 800 mL of blood in dependent vascular spaces in the lower extremities, with concomitant reduction in central venous pressure by 3 to 5 mm Hg and stroke volume by 50%. Resultant diminished baroreceptor stimulation leads to compensatory mechanisms including enhanced

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sympathetic and inhibited parasympathetic activity. Heart rate increases 10 to 25 beats per minute and sympathetic efferents to arterioles command an increase in peripheral resistance. Mean arterial blood pressure is preserved, assuring maintenance of homeostasis. Sudden pain, fear, and a host of other precipitants can momentarily defeat the delicate balance of homeostatic mechanisms, and syncope occurs. The term vasovagal syncope, coined by Lewis in 1932, refers to dual mechanism of loss of peripheral vasoconstriction (collapse of peripheral resistance) and cardioinhibition (vagus-induced bradycardia). Terms appearing in contemporary literature including neurally mediated, neuroregulatory, and neurocardiogenic syncope are synonymous. Lewis recognized that loss of peripheral resistance was the predominant mechanism in most instances of syncope. The term vasodepressor syncope denotes hypotension without significant bradycardia, whereas cardioinhibitory syncope refers to vagally induced bradycardia as the predominant mechanism. This is a clinically important distinction. The cardioinhibitory reflex can be powerful. Ventricular standstill and fibrillation have been reported with psychological stimuli. In contrast to vasodepressor syncope, cardiac syncope is sudden in onset. With asystole, presyncope occurs within several seconds and loss of consciousness within 6 to 8 seconds when upright. Injury and sudden death are attendant risks in malignant forms of cardioinhibitory syncope. When evaluating syncope, the evaluator must ask first ‘‘Is it syncope or something else?’’ The following historical points aid accurate diagnosis: 1. Postural setting: Syncope characteristically occurs when upright, less often while seated, and rarely in recumbency. Seizures do not respect posture. 2. Length of prodrome: In vasodepressor (noncardiac) syncope, there is usually a lengthy prodrome of 2 to 5 minutes. Feelings of uneasiness, warmth, anxiety, and queasiness are common during the prodrome, along with a desire for cool air and ventilation. In contrast, seizure auras, if present, are usually brief. 3. Antecedent symptoms: Visual complaints including pale, yellow, white, bleached, darkened, or constricted vision (‘‘tunnel vision’’) denote retinal ischemia, indicating an extracerebral mechanism for the event. Respiratory antecedents might include yawning or deep breathing. Gastrointestinal (GI) symptoms include an empty, hollow, or unsettled sensation in the epigastrium. Anxiety, dry mouth, and clamminess in the forehead and hands are common. Giddiness and lightheadedness may occur as the systolic blood pressure approaches 70 mm Hg, but, unlike true vertigo, there is no element of rotation of the environment or the body. 4. Syncopal episode: Syncope is a brief event, lasting 10 to 15 seconds, with little or no confusion. It is a hypotonic rather than rigid event (‘‘syncopal slump’’) with pallor (white—loss of color, rather than blue). Respirations are shallow and often imperceptible. Return of consciousness is rapid, as is alertness. The embarrassed victim may

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rise quickly only to repeat the episode. This feature is diagnostic of vasovagal syncope. 5. Convulsive accompaniments and urinary incontinence: In experimental syncope, the EEG background frequency slows, lowers in amplitude, and eventually becomes flat, devoid of activity, as syncope ensues. In 10% to 15% of fainters, brief myoclonic jerks of the face and hands, tonic posturing, or other brief seizure-like activity occurs. This phenomenon constitutes the convulsive accompaniment that may occur in syncope. This is not a seizure, which is characterized by excessive neuronal discharges rather than absence of cortical activity. This convulsive accompaniment rather reflects a state of functional decerebration. In addition, approximately 10% of fainters experience urinary incontinence, which, if coupled with convulsive accompaniments, may lead to an erroneous diagnosis of seizure or epilepsy in one third of cases. 6. The syncopal setting: The situation or the circumstances in which the event occurs is of utmost importance. Worry, emotional upset, medication, alcohol, physical exertion, dehydration, medical procedure, or other precipitants may be present. The evaluator, having determined that syncope has indeed occurred, must attempt to determine the cause or mechanism if possible. Table 16-1 lists potential causes of syncope. Fortunately 50% or more of syncope is benign and does not signify underlying disease. A careful history and physical examination may indicate the cause of syncope in 25% to 35% of fainters and in 75% of persons in whom a cause is found (7). Basic laboratory tests (complete blood count, chemistry panel) and 12-lead electrocardiogram (ECG) may provide an answer in 5% to 10% of patients. Further studies should be guided by the history and physical findings, and may direct one toward cardiac studies such as echocardiogram, Holter monitor, ambulatory event recording, or ultimately electrophysiological studies. Brain MRI and EEG studies are usually not helpful. When initial studies do not provide an explanation, headup tilt (HUT) table testing may be helpful in the evaluation of syncope. HUT may be positive in 50% of cases of syncope of unknown cause, supporting a vasovagal mechanism for the event. However, HUT without pharmacologic activation has a false-positive rate of approximately 10%, rising to 27% or more with pharmacologic activation (commonly nitroglycerine). False-positive studies have led to an incorrect diagnosis of syncope in individuals with clinical seizures. Other caveats involving HUT include nonstandard tilt angles, variable tilt duration, and lack of reproducibility in some studies. HUT is not recommended in the routine evaluation of syncope. Aeromedical disposition in syncope can be favorable in most instances in which a benign mechanism, that is not likely to recur in flight, can be demonstrated. Satisfactory exclusion of serious causes of syncope can be accomplished with appropriate testing, and a period of symptom-free observation might provide further assurance.

TABLE

16-1

Etiology of Syncope Reflex-mediated vasomotor instability Vasovagal (neurocardiogenic, neurally mediated, neuroregulatory) syncope: the common faint Situational syncope (related to a particular circumstance) Cough (tussive) syncope Sneeze Swallow Defecation Postmicturition syncope Weight lifting Exercise induced Trumpet player Mess trick Valsalva Medical procedure: physical examination (eyeoculovagal, ear, etc.), venipuncture, genitourinary or gastrointestinal instrumentation, etc. Hot tub or shower Orthostatic/dysautonomic Primary autonomic dysfunction (autonomic neuropathy, CNS disorders) Secondary autonomic dysfunction Medications, alcohol Prolonged illness, prolonged bedrest Hypovolemia (blood loss, dehydration) Impaired cardiac output Obstructive disease: aortic stenosis, idiopathic hypertrophic subaortic stenosis, pulmonary stenosis Pump failure: myocardial infarction, coronary artery disease, cardiomyopathy Impaired cardiac rhythm Bradycardias Tachycardias Mixed rhythm disturbances: sick sinus (brady/tachy) syndrome Psychiatric disease Miscellaneous Carotid sinus syncope Glossopharyngeal neuralgia Anemia Unknown Adapted from Benditt DG, Lurie KG, Adler SW, et al. Pathophysiology of vasovagal syncope, Table 1, 3; and Kapoor WN. Importance of neurocardiogenic causes in the etiology of syncope. Table 1, 56. In: Blann JJ, Benditt D, Sutton S, eds. Neurally mediated syncope: pathophysiology, investigations and treatment. The Bakken Research Center Series, Vol. 10. Armonk, NY: Futura, 1996; with permission. CNS, central nervous system.

Seizure Disorder Seizure disorder, convulsive disorder, and epilepsy are synonymous terms. A seizure is an abnormal, paroxysmal excessive discharge of cerebral neurons. Epilepsy is a chronic condition characterized by a tendency for recurrent (two or more), unprovoked seizures. The cumulative incidence

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of epilepsy is between 1.3% and 3.1% by age 80, with high incidence peaks in those younger than 20 and older than 60 (11). Epilepsy is idiopathic in two thirds of patients. Not all seizures represent epilepsy. All persons have a constitutional or genetically determined threshold for seizures, which if exceeded, leads to a clinical event. This threshold may fluctuate with time of day, hormonal influences, sleep deprivation, and other factors. Acute symptomatic seizures may occur with electrolyte disturbances (e.g., severe hypoglycemia or hyponatremia), infectious processes (e.g., pneumococcal meningitis with high-dose penicillin), and cardiac arrest with prolonged asystole and ensuing cerebral ischemia. Individuals with low-seizure threshold may experience seizures when exposed to medications (tricyclic antidepressants, bupropion, theophylline, and other medications). Additionally, some individuals with established epilepsy may achieve permanent remission (e.g., benign childhood epilepsy with centrotemporal spikes). For aeromedical purposes, a simple classification for seizures is adequate; it is presented in Table 16-2. Seizures are generalized from the onset in approximately half the cases and of partial onset in the remainder. Whereas generalized seizures are accompanied by simultaneous appearance of abnormal discharges throughout the cerebral cortex at onset, as the name implies, partial seizures (focal seizures in older terminology) arise in a discrete area of the cerebral cortex. This is significant in that a partial seizure implies a focal lesion, which must be identified (scar, tumor, abscess, cavernous angioma, other). In simple partial seizures, consciousness is preserved. Localized convulsive twitching of one hand might be caused from a lesion in the contralateral cerebral cortex. The individual remains alert, can carry on activity, and ordinarily suffers no after effects with cessation of the seizure. In complex partial seizures, consciousness is impaired or even lost. Complex partial seizures are commonly preceded by an aura of myriad descriptions. D´ej`a vu experiences, an unpleasant smell (olfactory aura) or taste (gustatory aura), a forced thought, vivid visual memory, or feeling of detachment from one’s self, may precede the seizure. The victim may engage in stereotyped movements such as repetitive lip-smacking, chewing movements, or hand or body movements such as fumbling with an object or rubbing

TABLE

16-2

Basic Classification of Seizures 1. Seizures that are generalized from the onset (e.g., idiopathic grand mal epilepsy, classic petit mal epilepsy) 2. Simple partial seizures with preservation of consciousness (e.g., focal motor seizure) 3. Complex partial seizures with alteration of consciousness (e.g., psychomotor seizure, temporal lobe automatism) 4. Partial seizures with secondary generalization (focal onset, progressing to generalized tonic-clonic seizure)

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a table. Awareness of surroundings is either compromised or lost, and one may or may not lose consciousness. Any partial seizure may spread to adjacent areas of cortex and eventually to deep-seated midline structures that project to all areas of the cerebral cortex, culminating in a generalized tonic-clonic (grand mal) seizure. For example, a focal seizure beginning in one hand as described earlier may spread to the forearm, upper arm, face, and leg (jacksonian march described by Hughlings Jackson), followed by collapse and a grand mal seizure. This is a partial seizure with secondary generalization. A generalized tonic-clonic seizure is announced by a tonic phase lasting 10 to 20 seconds, with brief flexion, then muscular rigidity with arms raised, abducted, partially flexed at the elbows, and externally rotated. Leg involvement is minor. Eyes remain open with upward deviation of the globes. Extension of the back and neck then follows, perhaps accompanied by an ‘‘epileptic cry’’ resulting from forced expiration through partially closed vocal cords. Arms and legs are extended, with apnea and cyanosis. The clonic phase then begins, which is in reality a rhythmic relaxation of tonic contractions. Clonic jerks become coarser and decline in frequency as relaxation phases lengthen. Tongue biting and urinary incontinence are common. Grand mal seizures are characteristically followed by a postictal state, which often includes a deep, snoring sleep. Return of consciousness follows with a confused and often combative arousal phase, which gradually clears. Nausea, vomiting, and headaches are common. Violent muscular contractions leave the trunk and extremity muscles sore and tender, and shoulder dislocations or vertebral compression fractures may occur. The victim wants to sleep, and upon returning to wakefulness is amnesic for the event. Petit mal (absence) seizures represent another variety of generalized epilepsy. Frequently appearing in childhood, petit mal seizures are characterized by brief lapse of awareness that may or may not be accompanied by myoclonic jerks and alterations of muscle tone. Brief loss of awareness, with repetitive eye flutter for 2 to 3 seconds, would be a representative example. The individual immediately resumes normal activity, and, if the spell is brief, may remain unaware of its occurrence. As with syncope, a careful history is of utmost importance in the evaluation of one or more seizures. Description by an observer might be the most important ingredient in accurate diagnosis. Records from paramedics and ambulance personnel, and detailed emergency room records including physician evaluations and nursing notes, may provide important details in accurately defining the clinical event. Personal history, family history, medication, and social history including alcohol and substance misuse are clearly important. Seizure evaluation, particularly in adults, must include brain MRI with and without gadolinium and a sleep-deprived wake and sleep EEG. Computed tomography (CT), even with contrast is insufficient because lesions such as mesial temporal sclerosis, hamartoma, or cavernous malformation

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might be overlooked. Wake-only EEG recordings are not sufficient because activation of a potentially epileptiform discharge might occur only during sleep recording. Photic stimulation is employed to elicit reflex-induced seizures (photic epilepsy) in susceptible individuals. It is important to note that up to 40% of individuals with epilepsy have normal EEGs throughout their lives, again emphasizing the importance of history. Clearly, a detailed evaluation is needed in the aeromedical disposition of persons with seizures or a question of seizures. A history of febrile seizures does not imply chronic seizure potential. Some persons with seizures achieve complete remission in adulthood, such as benign Rolandic epilepsy with centrotemporal spikes. Individuals with acute symptomatic seizures do not harbor chronic seizure potential. A thorough neurologic evaluation, at times coupled with a period of seizure-free and medication-free observation, may allow medical certification.

The Single Seizure A single unprovoked seizure does not constitute epilepsy unless it is followed by a second unprovoked event. An individual suffering a first-ever seizure should undergo a comprehensive general medical and neurologic evaluation. Degree of recurrence risk following a single unprovoked seizure can be related to risk factors. A history of febrile seizures or seizure occurrence in a first-degree relative elevates the risk, as does a history of remote neurologic insult or previous acute symptomatic seizure. An abnormal neurologic examination or abnormal imaging study is associated with increased risk of recurrence. EEG abnormalities are also important. Specifically, epileptiform abnormalities are associated with a 60+% risk of recurrence, nonspecific slowing with a 30% to 40% risk, and with a normal EEG 10% to 25% risk (12,13). Absent risk factors, recurrence risk is in the 26% to 33% range over 5 years (12), after which recurrence risk approximates that of the normal population. Most epileptologists elect not to treat individuals with a firstever seizure and no risk factors because the majority would be treated unnecessarily. This is important for the aviator because a 5-year period of seizure-free and medicationfree observation might allow consideration for aeromedical recertification. Initial treatment with anticonvulsants delays the process. A second seizure during that period satisfies the criteria for epilepsy (two or more unprovoked seizures), and recurrence risk following a second seizure escalates to 73%.

CEREBROVASCULAR DISEASE Stroke is the third leading cause of death in the United States and a major contributor to disability. Approximately 700,000 strokes occur in the United States annually, of which 200,000 are recurrent strokes. Approximately 85% of strokes are ischemic, whereas the remaining are hemorrhagic.

Ischemic Stroke Ischemic stroke may be classified based on the presumed nature of focal brain injury and the type and localization of the vascular lesion (11). Major categories include large artery atherothrombotic infarction (extracranial, intracranial, or cardioembolic), small vessel disease, other causes (dissection, hypercoaguable states), and stroke of indeterminate cause. Approximately 20% to 30% of strokes are cardioembolic. Large vessel disease is responsible in 15% to 20% of cases, 75% of which is extracranial in origin (carotid or vertebral arteries, aorta), the remainder arising from intracranial large vessels (intracranial portions of major arteries, basilar, anterior, middle, and posterior cerebral arteries and major branches). Small vessel disease (lacunar stroke) comprises approximately 20% stroke cases (12). Coagulation disorders account for 1% to 5% of cases of stroke, and stroke without demonstrable cause (cryptogenic stroke) occurs in a significant proportion of stroke victims. The aeromedical physician must address the issue of stroke in terms of primary prevention, secondary prevention, assessment of degree of significant functional disability, and determination of recurrence risk. Nonmodifiable risk factors for stroke include age (risk doubles in each decade for those older than 55 years), gender (males have higher risk than females), race (African Americans and Hispanics have higher risks than whites), and genetics (family history may increase risk). Well-documented modifiable risk factors for stroke include prior TIA/stroke, hypertension, diabetes, tobacco use, dyslipidemia, cardiac disease, atrial fibrillation, and asymptomatic carotid stenosis. Additional factors not fully supported by rigorous science include alcohol and drug abuse, physical inactivity, impaired nutrition, hypercoaguable states, elevated homocysteine, hormone replacement therapy, and oral contraceptives. Primary prevention of stroke involves vigorous attention to modifiable risk factors, which includes treatment of hypertension, physical exercise, addressing dyslipidemia with diet and/or medication, smoking cessation, avoiding excess alcohol ingestion, and detection and treatment of cardiac disease and significant asymptomatic carotid artery stenosis. Stringent diabetes management is important if the disease is present. Secondary prevention following ischemic stroke involves identification and mitigation of modifiable risk factors (13). Hypertension contributes to a variety of ischemic stroke subtypes through atherosclerosis, small vessel lipohyalinosis, and cardiac impairment. Effective management of hypertension alone can reduce stroke incidence by as much as 70% (14). In the PROGRESS trial, a combination of perindopril and indapamide produced a 43% reduction in recurrent stroke risk without regard to initial blood pressure (15). The seventh report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure (JNC-7) classifies blood pressure of less than 120/less than 80 as normal, 120–139/80–89 as prehypertension, 140–159/90–99 as hypertension stage I, and 160/100 or

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greater as hypertension stage 2 (16). Lifestyle modifications including weight control, physical activity, and moderation of sodium intake are recommended for persons with prehypertension. Along with lifestyle modifications, guidelines recommend thiazide-type diuretics, perhaps combined with a single agent for stage I hypertension, and for stage II hypertension two-drug combination for most (thiazide-type diuretic along with an angiotensin-converting enzyme inhibitor, angiotensin receptor blocker, β-blocker, or calcium channel blocker). Hyperlipidemia elevates stroke risk, particularly carotid artery–related strokes (17). American Stroke Association (ASA) guidelines recommend adopting National Cholesterol Education Program guidelines, which advise lifestyle modification, dietary changes, and medication for TIA or stroke patients with elevated cholesterol, comorbid cardiac disease, or evidence of atherosclerotic origin. Diabetes is a clear risk factor for stroke, being present in 15% to 33% of ischemic stroke victims. Additionally, smoking is a highly significant independent risk factor for ischemic stroke. It is generally accepted that heavy alcohol consumption elevates stroke risk in all subtypes, with perhaps a protective effect in light to moderate drinkers, such as 1 to 2 ounces daily. Less well-documented evidence exists for obesity and physical inactivity. ASA guidelines advocate carotid endarterectomy for symptomatic (TIA or stroke) patients with severe carotid stenosis (70%–99%), and in selected patients with 50% to 69% stenosis. Asymptomatic carotid stenosis is receiving increased attention along with treatment options. In unselected populations, 7% of men and 5% of women older than 65 years have greater than 50% carotid artery stenosis. The risk of stroke with greater than 60% stenosis is approximately 2% per year, with a myocardial infarction risk of approximately 5% per year (18). Treatment of asymptomatic carotid stenosis is controversial. Dodick et al. recommend consideration of carotid endarterectomy in patients with asymptomatic carotid artery stenosis only for medically stable patients with stenosis of 80% or greater who are expected to live for 5 years, and then only with surgeons who have a perioperative complication rate of less than 3% (19). Evidence-based guidelines for clinicians put forth by the American Academy of Neurology support these parameters for patients aged between 40 and 75 with 60% to 99% stenosis. Atrial fibrillation is associated with significant risk of cardioembolic stroke. Trials have shown a relative risk reduction of 68% and an absolute reduction in annual stroke rate from 4.5% to 1.4% in patients treated with dose-adjusted warfarin. Along with primary and secondary prevention strategies and assessment of residual neurologic deficit for functional significance, the evaluator must address recurrence risk for aeromedical disposition. In terms of overall risk, up to 30% of persons suffering ischemic stroke will suffer recurrent stroke within 5 years (18). In the Northern Manhattan Stroke Study (NOMASS) involving a mixed ethnic cohort (40% black, 34% Hispanic, 26% white) older than age 39, stroke recurrence

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risk was 25% at 5 years (20). Survival was better with lacunar stroke. Dhamoon et al. reported an 18.3% risk of recurrent stroke over 5 years (mean age 69.7 and mean follow-up 4 years) (21). In the Perth Community Stroke Study reporting 10-year risk of first recurrent stroke, the recurrence risk was 43%, risk being highest within the first year and averaging 4% per year after the first year (22). Numbers were not large. Of 328 patients (69% with ischemic stroke), 30 persons suffered recurrent stroke in the first year, and 34 over the next 9 years. Predictors of recurrent stroke included increasing age, atrial fibrillation, high alcohol consumption, hemorrhagic stroke, and hypertension at the time of discharge. In a Spanish study (mean age 75.4 years), cumulative risk was 26% at 5 years, with age being the major predictor (23). In a British study, 5-year risk of recurrent stroke was 16.6% (24). Recurrence risk varies with stroke subtype, an important consideration in aeromedical disposition. In a follow-up of at least 10 years of 178 patients with lacunar stroke, recurrent stroke occurred in 23.5% (annual risk of 2.4%) (25). Stroke in the young warrants specific attention because recurrence risk may be lower compared to adults and etiology may vary. In a 5-year follow-up of 95 patients younger than 45 years, 4.7% suffered recurrent stroke (26). In the Baltimore-Washington Cooperative Young Stroke Study of 428 first strokes in persons aged 15 to 44, approximately 34.3% had stroke of indeterminate cause and another 18.7% had no probable cause but at least one possible cause (27). Identifiable causes included cardiac embolism (31.1%), hematologic/other causes (19.8%), nonatherosclerotic vasculopathy (11.3%), illicit drug use (9.4%), and migraine (1.4%). Large artery atherosclerotic disease accounted for only 3.8%. In a Spanish study of 272 young adults aged 15 to 45 with first-ever ischemic stroke, annual stroke recurrence rate was 3.6% during the first year, declining to 1.7% annually thereafter (28). In an Italian study of 60 patients aged 17 to 45 with TIA or ischemic stroke, recurrence rate was 7.4% over a mean span of 6.1 years (29). Ischemic stroke of indeterminate cause (cryptogenic stroke) comprises a significant proportion of stroke (30%–40%) (30). Medical information doubles within 10 years, and a MEDLINE search of cerebrovascular disorders from 1966 to 2004 generates more than 170,000 results (31). The evaluator seeking best evidence for aeromedical disposition in strokes must consider a large body of evidence outside his or her medical discipline. A principle of individual consideration utilizing best available evidence should be followed. Louis Caplan, Professor of Neurology at Harvard University who specializes in cerebrovascular disease, offered the following advice (personal communication, 2002): ‘‘My bias is and always has been that strokes are very heterogeneous and that the risk of recurrent strokes and seizures after stroke and cardiac risk varies with the etiology, nature, and location of the stroke in the individual. My advice would be to write no firm general rule, but to evaluate each individual case—preferably by a panel of individuals who specialize in stroke.’’

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Hemorrhagic Stroke Intracerebral hemorrhage (bleeding into brain parenchyma from an arterial source) is associated with hypertension in 72% to 81% of cases (32). Sites of bleeding include pons, cerebellum, basal ganglia, and lobar (subcortical white matter). Death or severe disability is common, ordinarily precluding return to flying. Nonhypertensive causes of intracerebral hemorrhage include vascular malformations such as subdural hematomas or arteriovenous malformations, amphetamine use, cerebral amyloid angiopathy, vasculitis, and hemorrhage into metastatic tumor. Malignant melanoma is the third most common metastatic lesion to the brain following breast and lung, and hemorrhage is common. Prognosis following intracerebral hemorrhage is not uniformly poor, and good recovery may be achieved with identification and idealization of risk factors or surgery. Judicious treatment of hypertension might reduce recurrence risk to an acceptable level. Complete resection of a vascular malformation may be curative following intracerebral hemorrhage, but seizure risk must be addressed. Although most malformations present with hemorrhage, a significant proportion (32%) are associated with seizures (33). Seizures tend to be associated with large malformations involving the cerebral cortex. Although complete surgical resection may eliminate risk of hemorrhage, risk of seizures arising from the surrounding neuronal bed might remain and preclude certification.

Intracranial Aneurysms The most frequent cause of nontraumatic subarachnoid hemorrhage, accounting for 80% of cases, is a ruptured intracranial secular aneurysm (34). Prevalence of aneurysms greater than 3 mm in diameter has been reported in 4% of autopsies. Aneurysms commonly arise from major arteries at the base of the brain (circle of Willis) and are thought to arise from a combination of congenital defects in the muscular wall of the artery and degenerative changes injuring the internal elastic lamina. They involve the anterior circulation (anterior and middle cerebral artery distributions) in more than 80% of cases and are multiple in 31%. Mortality from ruptured aneurysms is 23%, and significant disability is present in more than 50% of survivors.

TABLE

If an aneurysm is surgically isolated from the circulation and no others exist, the patient is cured. Conventional transfemoral cerebral angiography performed 3 to 12 months following surgery demonstrates cure. At times aneurysmal anatomy (e.g., fusiform or broad-necked aneurysm) precludes clipping, and noncurative procedures such as wrapping or use of glue are employed. Risk of bleeding, though perhaps lessened, remains. The aeromedical evaluator’s primary concern is residual neurologic impairment, which might include focal neurologic deficit or cognitive impairment. Careful neurologic evaluation is warranted, and an observation period of 1 year is commonly prescribed. At times angiography does not demonstrate a source of bleeding despite multiple procedures. If an individual with idiopathic subarachnoid hemorrhage has no recurrence within 1 year, risk of further bleeding is acceptably low.

TRAUMATIC BRAIN INJURY Traumatic brain injury (TBI) is a frequent cause of neurologic disability in the 20 to 55 age-group and is commonly encountered in aviators. The aeromedical evaluator is not concerned with acute management, but rather the possibility of persistent residual neurologic impairment. Essential ingredients in the evaluation of aviators with TBI include determination of the nature and severity of TBI. Medical records will disclose the nature of TBI. Concussion is characterized by transient loss or alteration of consciousness (seconds to hours) caused by a blow to the head without evident tissue destruction. However, there may be microscopic injury, and petechial hemorrhage, axonal shearing with retraction bulbs, and edema may occur. Frank injury to brain parenchyma may occur through brain contusion, diffuse edema, laceration or penetration by a foreign object, and hemorrhage within the brain substance (intracerebral hematoma). Additionally, extraparenchymal bleeding (subdural or epidural hematoma) may cause cerebral injury through compression and herniation mechanisms. Severity of TBI can be assessed utilizing the Glasgow Coma Scale (Table 16-3) and duration of posttraumatic amnesia (PTA) (Table 16-4). A Glasgow Coma score of 13 to 15

16-3

Glasgow Coma Scale Eye Opening

E

Best Verbal Response

V

Best Motor Response

M

Spontaneous To voice command To pain stimuli No response

4 3 2 1

Oriented and converses Confused Inappropriate words Incomprehensible sounds No sounds

5 4 3 2 1

Obeys commands Localizes to pain Withdraws from pain Decorticate (flexion) posturing Decerebrate (extension) posturing No response

6 5 4 3 2 1

E + V + M = 3 to 15.

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TABLE

16-4

Posttraumatic Amnesia (PTA) Mild brain injury Moderate brain injury Severe brain injury Very severe brain injury

0–1 hr of PTA 1–24 hr of PTA 1–7 d of PTA Beyond 7 d of PTA

denotes mild TBI, a score of 9 to 12 moderate TBI, and below 3 to 8 severe TBI by these criteria. When Glasgow Coma score and duration of PTA are coupled with records documenting the clinical course during the acute recovery period, the evaluator can accurately determine the severity of TBI. A Glasgow Coma score below 9 and/or PTA greater than 24 hours should heighten concern for persistent neurologic impairment. Sequelae of TBI include postconcussion syndrome, focal neurologic deficit, neuropsychological residual, and posttraumatic epilepsy (PTE).

Postconcussion Syndrome Postconcussion syndrome is a nonspecific constellation of symptoms that commonly follow minor or seemingly inconsequential head injury, perhaps without loss of consciousness. Symptoms include headache, irritability, inability to concentrate, inattention, insomnia, memory difficulty, and nonspecific dizziness. Neurologic examination and imaging studies are normal. In most individuals, symptoms are self limited, lasting days to weeks or at most 3 to 6 months. This syndrome ordinarily does not pose long-term implications for the aviator.

Focal Neurologic Deficit Focal neurologic deficit following TBI can take many forms, including cranial nerve palsies (olfactory nerve, optic nerve, nerves to extraocular muscles, facial nerve, acousticovestibular nerve, other), expressive aphasia, hemiparesis or other focal motor deficit, and ataxia. Most neurologic recovery occurs within 6 months, with further recovery occurring more slowly over a span of 2 to 3 years.

Neuropsychological Residual Accelerative and rotational forces can injure brain tissue exposed to irregular bony surfaces within the cranial vault. The frontal poles and orbitofrontal surfaces of the frontal lobes may suffer contusion injury, and the anterior temporal lobes are similarly susceptible. The frontal lobes have to do with personality, behavior, and executive functions, whereas the temporal lobes are more related to intellect and memory. Frontal lobe injury may lead to behavioral changes including disinhibition, irritability, and impaired anger control with explosive outbursts. Alternatively, an individual might exhibit apathy, indifference, and depression. Impaired judgment, planning, reasoning, abstraction, and initiation of activity may reflect impaired executive functions. Perseveration (inability to

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change mental set) and inability to employ a problem-solving strategy are common. Deep white matter injury may cause impaired attention and concentration. Temporal lobe injury may lead to significant memory impairment, which is often a major sequela of TBI. The aeromedical evaluator should remain mindful of the possibility of neuropsychological impairment in persons with moderate to severe TBI. If indicated by clinical evaluation and review of records, formal neuropsychological testing might be needed.

Posttraumatic Epilepsy A major aeromedical concern following TBI is risk of seizures. Whereas penetrating injuries involving dural laceration and violation of brain parenchyma confer a 20% to 40% risk of PTE, risk in closed head injury is approximately 5%. A history of febrile seizures, family history of seizures in a first-degree relative, cerebral contusion, and hematoma (epidural, subdural, intraparenchymal) are associated with increased risk for PTE. An impact seizure, occurring as the name implies at the time of contact, ordinarily does not portend chronic seizure potential. Delayed seizures beginning weeks or months after TBI imply gliotic scar with risk of persistent seizure potential. Risk of PTE increases with head injury severity (35), particularly with severe TBI. In this study by Annegers, 1-year risk with severe TBI was 6%, compared to less than 1% with mild to moderate TBI. Cerebral cortical contusion, cerebral hematoma, early seizures, loss of consciousness or PTA beyond 1 day, and depressed skull fracture are associated with increased seizure risk. The presence of subdural hematoma confers increased risk, as well as epidural hematoma to a lesser extent. Iron compounds are important in animal models of epileptogenesis. Current thought reflects the hypothesis that PTE is an ‘‘iron-driven’’ phenomenon. The theory holds that extravasated red blood cells into neural tissue eventually leads to iron liberation from hemoglobin and formation of highly reactive free radical oxidants in the metabolism of iron, resulting in lipid peroxidation with injury to the cell membrane and cell organelles. Approximately one third of individuals with PTE will have a first event within 3 months, 50% within 6 months, 75% within 1 year, and 90% within 2 years.

NEOPLASMS Intracranial neoplasms will be encountered in aviators. Presenting symptoms of tumors may include headaches, vomiting, seizures, cognitive changes, and focal neurologic symptoms such as hemiparesis or ataxia.

Benign Neoplasms Benign intracranial neoplasms can involve the dura, cranial nerves, or brain parenchyma (36). Extraparenchymal tumors

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include meningioma, acoustic neuroma, neurofibroma, and pituitary adenoma. Benign parenchymal tumors include ependymoma, colloid cyst of the third ventricle (in reality a cyst), and choroid plexus papilloma. Symptoms usually arise from compression of neural structures rather than invasion. Some benign lesions cannot be safely removed for fear of compromising major or vital structures, giving rise to the term malignant by position. These may include tumors involving the clivus, the cavernous sinus, and craniopharyngiomas adherent to the floor of the third ventricle. Residual tumor may lead to recurrence. Benign dura-based tumors or cranial nerve tumors lend themselves to complete resection, particularly if removed when small. These include meningiomas overlying the cerebral cortex, acoustic neuroma, trigeminal neurofibroma, and pituitary adenoma. Colloid cysts, choroid plexus papillomas, and pinealomas can often be totally removed.

Malignant Neoplasms Malignant intracranial neoplasms usually arise in brain parenchyma, are invasive, and have potential for rapid growth when of high grade. The gliomas (astrocytomas and oligodendrogliomas) are the most common malignant primary parenchymal tumors. The term glioblastoma multiforme refers to high-grade astrocytomas. Invasive features include finger-like projections of malignant cells that interdigitate with normal neural tissue. The surgeon can ‘‘debulk’’ the tumor, but cannot employ the principle of wide excision without compromising neurologic function. Recurrence is the rule with gliomas, albeit possibly many years later when the tumor is of low grade. Surgical removal without recurrence is uncommon. There are exceptions, such as cystic astrocytoma of the cerebellum with mural nodule in children. For aeromedical disposition, the evaluator must consider the nature (benign or malignant) and location of the tumor, the presenting signs, the nature and degree of residual deficit (motor, sensory, cognitive), potential for recurrence, and the possibility of seizures. As with resection of vascular malformations, complete tumor resection does not assure freedom from seizures, which may continue to arise from the altered neuronal bed of the lesion. Often a period of observation is employed. Despite apparent neurologic stability over a long period, even years, with low-grade gliomas, malignant parenchymal tumors characteristically recur, ordinarily barring medical certification.

HEREDITARY, DEGENERATIVE, AND DEMYELINATING DISORDERS Included here for discussion are several conditions that may be nonprogressive, intermittently active and cumulatively progressive, or follow a slowly progressive temporal profile. With appropriate monitoring, medical certification may be appropriate unless and until the condition compromises aviation safety.

Familial and Essential Tremor Essential tremor is the most common movement disorder with a reported prevalence of up to 5.6%. Familial tremor and essential tremor are the same, the only difference being the presence or absence of a family history of tremor. Autosomal dominant inheritance is present in 60% of cases (37). Although tremor may appear early in life, the mean age of onset is 35 to 45 years. Hand tremor is present in 94%, head tremor in 33%, voice tremor in 16%, and leg tremor in 12%. Slow worsening of tremor over many years is a characteristic feature. Tremor is usually postural (voluntarily maintaining posture against gravity, such as arms outstretched) and with intention or use (directed voluntary movement toward a target). The tremor frequency is 8 to 12 Hz. Victims often describe difficulty in writing, balancing peas on a fork or soup on a spoon, carrying an empty cup on a saucer, using a screwdriver, or bringing a glass to the mouth. Rest tremor rarely occurs. Improvement with alcohol ingestion is commonly reported. Essential/familial tremor may have aeromedical implications (e.g., difficulty targeting and manipulating small closely spaced cockpit switches). One of my patients, an airline captain, noted a vigorous shudder in his aircraft as he applied toe brakes after landing. He shut down the aircraft and had it towed to the gate, assuming a mechanical problem. Nothing was found, but recurrence on two other occasions led to identification of a foot tremor. Low-dose β-blocker treatment allowed him to complete his career. Fortunately tremor causes little or no impairment in most individuals, progressing very slowly and perhaps not requiring treatment. If treatment is warranted, β-blockers are often highly effective. Primidone, an older anticonvulsant, is useful in pediatric dose ranges. However, primidone is a barbiturate derivative that can cause drowsiness, barring its use in the aviation environment. Gabapentin and benzodiazepines are also precluded because of potential central nervous system effects.

Parkinson’s Disease Parkinson’s disease is characterized by a classic triad of symptoms including tremor at rest, muscular rigidity, and slowness of movement (bradykinesia). Common clinical features include a slow-shuffling gait, freezing or gait arrest, a general attitude of flexion, impaired postural reflexes, diminished vocal volume, and paucity of facial expression (mask-like facies). These features are observed by the examiner, and neurologic examination usually discloses cogwheel rigidity and impaired rapidly alternating movements (foot tapping, finger wiggle, pronation–supination). An individual may seek medical attention early in the course of the illness for purposes of identifying the condition, but with no desire or need for treatment. Aeromedical certification may be allowed with appropriate monitoring mechanisms for progression. When treatment is indicated, potential side effects of medication warrant consideration.

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Anticholinergics, with their attendant risk of drowsiness and cognitive changes, were the only agents available for treatment until the advent of levodopa in the late 1960s. Levodopa remains the gold standard treatment, and many individuals function well with this agent, remaining relatively free of side effects. In later years, dopamine agonists, primarily pramipexole and ropinirole, came into favor as initial treatment, adding levodopa later if necessary. These agents were initially approved for use by the Federal Aviation Administration (FAA), but due to reports of excessive daytime sleepiness approval was withdrawn. Amantadine has been employed for treatment of tremor, and entacapone delays the breakdown of dopamine in individuals taking levodopa. Some individuals with Parkinsonian symptoms exhibit evidence of a more widespread cerebral disturbance, giving rise to the term Parkinson-plus syndromes. Additional features may include dementia, impaired eye movements, ataxia, orthostatic hypotension, and dysautonomic manifestations. Multiple system atrophy and progressive supranuclear palsy are examples. The neurologist or movement disorder subspecialist differentiates these entities based on clinical features. Early or mild Parkinson’s disease causing little or no impairment need not preclude medical certification. Some medications, such as levodopa or amantadine, might be acceptable without significant side effects.

Multiple Sclerosis MS is a chronic disease affecting young- and middle-aged adults with slight female preponderance. The illness is characterized by multiple lesions of the nervous system, separated by space and by time. Lesions in MS consist of plaques, localized areas of inflammation, demyelination, and glial scarring involving the white matter of brain and spinal cord. Episodes of demyelination and remyelination account for the exacerbations and remissions commonly seen in MS. The clinical course of MS may vary among individuals. In primary progressive MS, the disease follows a slowly progressive clinical course without interruption. In the more commonly encountered relapsing and remitting variety of MS, the characteristic exacerbations and remissions occur. Each exacerbation may incompletely resolve, resulting in cumulative neurologic deficit. In secondary progressive MS, a relapsing and remitting clinical course gives way to a slowly progressive decline in neurologic function in later years. Clinical manifestations of MS can be highly variable depending on plaque distribution in brain and spinal cord. Unilateral optic neuritis is a common presenting sign of MS. Other symptoms might include diplopia, dysarthria, ataxia, motor or sensory symptoms, and bladder or bowel dysfunction. Approximately 14% of individuals with MS have mild or inconsequential neurologic deficit, giving rise to the term benign MS. Acute exacerbations are commonly treated with intravenous corticosteroids, specifically methylprednisolone. Immunomodulatory therapy is employed in an effort to reduce the frequency and severity of exacerbations and slow

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the accumulation of neurologic deficit. Therapy consists of parenteral administration of an interferon preparation or glatirimer acetate. In individuals with significant progression despite steroids and immunomodulatory therapy, chemotherapeutic agents may be employed and agents that are prescribed include cyclophosphamide, azothioprine, methotrexate, and novantrone. Aeromedical disposition may be favorable in some individuals with MS. Persons with ‘‘benign MS’’ may present no risk to aviation safety. Some with slowly progressive MS, and others with widely separated and relatively minor exacerbations without accumulation of significant neurologic deficit might warrant consideration. Others with significant functional disability, symptoms clearly related to aviation safety (e.g., vertigo, diplopia, cognitive change, etc.), or frequent severe exacerbations will not be candidates for medical certification.

CAVEATS IN NEUROLOGIC AEROMEDICAL DISPOSITION In neurologic diagnosis, a frequently occurring and vexing problem is the proper interpretation of ancillary studies. This is of utmost importance in aeromedical disposition because an inadequate or inaccurate history coupled with a misinterpreted laboratory study can erroneously hamper or end an aviation or space career. Interpretations that commonly confound neurologic diagnosis include those of HUT, EEG, and MRI studies.

Head-Up Tilt Studies As mentioned in the section Syncope in this chapter, HUT studies may aid the evaluation of unexplained syncope. Kapoor reported approximately 50% of patients with unexplained syncope have a positive response to passive tilt testing (38). In that study, two thirds of positive responses occurred with pharmacologic activation (isoproterenol) as opposed to passive tilt. However, a significant proportion of asymptomatic individuals may have a positive response. Kapoor and Brant reported a false-positive rate of 20% without pharmacologic evaluation and 31% with isoproterenol activation (39). Reproducibility is another issue. In a study involving 109 subjects undergoing HUT on 2 consecutive days, Brooks et al. reported a high degree of variability in responses to HUT, with frequent nonreproducibility of vasodepressor responses on the second day (40). Reproducible vasodepressor responses occurred in only 11 of 36 subjects (31%). The aeromedical evaluator must be cautious in coupling a false-positive tilt table response with a nonsyncopal neurologic event, such as seizure. Such errors have occurred.

Electroencephalogram In the general population, there is a 10% to 15% incidence of minor nonspecific EEG abnormalities, and 2% to

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3% of the population demonstrates moderate abnormalities (41). These changes may also occur in the presence of disease, and careful clinical judgment is necessary in determining their significance, if any. The aerospace medicine physician must be particularly cautious when attempting to couple reported EEG abnormalities with clinical events. For example, a nonspecific EEG abnormality appearing in an individual with syncope accompanied by twitching and incontinence may lead to an erroneous diagnosis of epilepsy with its far reaching implications. The aeromedical evaluator must keep in mind that individuals without seizures may demonstrate epileptiform abnormalities on EEG, whereas individuals with epilepsy (fits) may have persistently normal EEGs (spikes without fits and fits without spikes). Engel notes that 2% of the population demonstrates specific epileptiform abnormalities on EEG (42). This may lead to an inappropriate diagnosis of epilepsy. It is well known that a significant proportion of individuals with epilepsy have a normal EEG (42–44). Studies in the literature report that 50% to 60% of routine EEGs (30-minute routine recordings without sleep deprivation), obtained after a seizure in patients later clearly diagnosed as having epilepsy, demonstrate epileptiform abnormalities (45). Activation techniques including hyperventilation, photic stimulation, sleep recording, and sleep-deprived recording may increase the yield. Interictal EEG abnormalities may be intermittent, and a 30-minute recording is a small sample of a 24-hour day. Serial EEG recordings may also increase yield, but little further yield is obtained after four recordings (46). It is important for the EEG interpreter to state that a normal EEG does not exclude the possibility of epilepsy, as well as mentioning sampling effect (47). In difficult cases, sustained video-EEG recording (days or more) can be accomplished in an epilepsy monitoring unit. Lastly, there are known benign EEG patterns with epileptiform morphology that might be interpreted by lessexperienced clinicians as being significant. Examples include 14 and 6 Hz positive spikes, small sharp spikes, 6 Hz spike and wave, and wicket spikes (47). These patterns can be seen in normal individuals.

Magnetic Resonance Imaging A frequently occurring finding in cerebral MRI is the presence of T2 hyper intense lesions, commonly referred to as unidentified bright objects (UBOs), or nonspecific white matter hyperintensities (WMHs). The reporting of these lesions may lead to diagnostic uncertainty for the aeromedical examiner (AME)/flight surgeon and have far reaching implications for the aviator or astronaut if interpreted wrongly. A fully trained and experienced neuroradiologist might report ‘‘normal’’ findings, whereas other interpreters might report concern for small vessel cerebrovascular disease (multi-infarct state) or demyelinating disease (MS). In one study, UBOs were present in 5.3% of healthy individuals aged 16 to 65, but were less common in younger

individuals (48). In another study, pathologic features of T2 silent WMHs in patients without neurologic signs or symptoms represented myelin pallor associated with vessels showing hypertensive and arteriosclerotic changes (49). Others feel the lesions represent dilated normally occurring perivascular (Virchow-Robin) spaces. UBOs occur with greater frequency in individuals with migraine (50). The neurologic literature reflects considerable debate regarding the nature and significance of UBOs. The debate is also reflected in practice, as evidenced by variable interpretations among general radiologists, neuroradiologists, neurologists, and neurosurgeons. The aeromedical evaluator with less frequent exposure to MRI is further disadvantaged. One can only advise that the ability to distinguish between nonspecific WMHs (UBOs, WMHs) and diseasespecific white matter lesions is an important consideration for the clinician. As in other ancillary studies, the test must be interpreted in the context of the patient and the clinical setting.

REFERENCES 1. Wiebers DO, Dale AJ, Kokmen E, et al. eds. Mayo clinic examinations in neurology, 7th ed. St. Louis: Mosby, 1998:3. 2. Raskin NH. Paroxysmal disorders: migraine and other headaches. In: Rowland LP, ed. Merritt’s textbook of neurology, 9th ed. Baltimore: Williams & Wilkins, 1995:838. 3. Trimble MR. Psychiatry and neurology: neurologic presentations of psychiatric illness. In: Aminoff MJ, ed. Neurology and general medicine. 2nd ed. New York: Churchill Livingstone, 1995:482. 4. Hodges JR. Transient amnesia, clinical and neuropscyhological aspects. London: WB Saunders, 1991. 5. Dermkasian G, Lamb LE. Syncope in a population study of healthy young adults. JAMA 1958;168:1200–1207. 6. Grow MC, Armstrong HG. Fit to fly. New York: D. AppletonCentury, 1942:62. 7. Olashanksy B. Syncope: overview and approach to management. In: Grubb BP, Olshansky B, eds. Syncope: mechanisms and management. New York: Futura Publishing, 1998:33. 8. Hauser WA, Hesdorffer DC. Incidence and prevalence. Epilepsy: frequency, causes and consequences. New York; Demos, 1990:1. 9. Hauser WA, Rich SS, Annegers JP, et al. Seizure recurrence after a first unprovoked seizure: an extended follow up. Neurology 1990;40:1163–1170. 10. Van Donselaar CA, Schimisheimer RJ, Geerts AT, et al. Value of the electroencephalogram in adult patients with untreated idiopathic first seizures. Arch Neurol 1992;49:231–237. 11. Sacco RL, Adams R, Albers G, et al. Guidelines for prevention of stroke in patients with ischemic stroke or transient ischemic attack: a statement for health care professionals from the American Heart Association/American Stroke Associationn council on stroke. Stroke 2006;37:577–617. 12. Fleming KD, Brown RD, Petty GW, et al. Evaluation and management of transient ischemic attack and minor cerebral infarction. Mayo Clin Proc 2004;79(8):1071–1086. 13. Fleming KD, Brown RD. Secondary prevention strategies in ischemic stroke: identification and optimal management of modifiable risk factors. Mayo Clin Proc 2004;79(10):1330–1340. 14. Gorelick PB. Stroke prevention. Arch Neurol 1995;52:347–355. 15. PROGRESS Collaborative Group. Randomized trial of Perindopril based blood-pressure-lowering regimen among 6,105 individuals with previouis stroke or transient ischemic attack. Lancet 2001;358:1033–1041.

CHAPTER 16 16. Chobanian AV, Bakris GL, Black HR, et al. National high blood pressure education program coordinating committee. The seventh report of the Joint National Committee on Prevention, Detection, Evaluation and Treatment of High Blood Pressure: the JNC-7 report. JAMA 2003;289:2560–2572. 17. Fine-Edelstein JS, Wolf PA, O’Leary DG, et al. Precursors of extracranial carotid atherosclerosis in the Framingham study. Neurology 1994;44:1046–1050. 18. Wilterdink JL, Furie KL, Easton JD. Cardiac evaluation of stroke patients. Neurology 1998;51(Suppl 3):S23–S26. 19. Dodick DW, Meissner I, Meyer FB, et al. Evaluation and management of asymptomatic carotid artery stenosis. Mayo Clin Proc 2004;79(7):937–944. 20. Sacco RL, Shi T, Zamanillo MC, et al. Predictors of mortality and recurrence after hospitalized cerebral infarction in an urban community: the Northern Manhatton stroke study. Neurology 1994; 44(4):626–634. 21. Dhamoon MS, Sciacca RR, Rundek T, et al. Recurrent stroke and cardiac risks after first ischemic stroke: the Northern Manhattan study. Neurology 2006;66(5):641–646. 22. Hardie K, Hankey GJ, Jamrozik K, et al. Ten-year risk of first recurrent stroke and disability after the first-ever stroke in the Perth Community Stroke Study. Stroke 2004;35:731–735. 23. Modrego PJ, Mainar R, Turull L. Recurrence and survival after first-ever stroke in the area of Bajo Aragon, Spain. A prospective cohort study. J Neurol Sci 2004;224(1–2):49–55. 24. Hillen T, Coshall C, Tilling K, et al. Cause of stroke recurrence is multifactorial: patterns, risk factors, and outcomes of stroke recurrence in the South London stroke register. Stroke 2003;34(6):1457– 1463. 25. Staaf G, Lindgren A, Norrving B. Pure motor stroke from presumed lacunar infarct: long-term prognosis for survival and risk of recurrent stroke. Stroke 2001;32(11):2592–2596. 26. Ory F, Albucher JF, Guiraud-Chaumeil B, et al. Risk of recurrent stroke in adults aged under 45 years following a first ischemi stroke: a five-year study of 95 patients. Rev Neurol 2003;159(8–9):755–760. 27. Kittner SJ, Stern BJ, Wozniak M, et al. Cerebral infarction in young adults. The Baltimore-Washington cooperative young stroke study. Neurology 1998;50:890–894. 28. Verona JF, Bermejo F, Guerra JM, et al. Long-term prognosis of ischemic stroke in young adults. Study of 272 cases. J Neurol 2004;251(12):1507–1514. 29. Musolino R, La Spina P, Granata A, et al. Ischemic stroke in young people: a prospective and long-term follow up study. Cerebrovasc Dis 2003;15(1–2):121–128. 30. Sacco RL, Ellenberg JH, Mohr JP, et al. Infarcts of undetermined cause: The NINCDS stroke data bank. Ann Neurol 1989;25:382–390. 31. Demaershcalk BM. Literature-searching strategies to improve the application of evidence-based clinical practice principles to stroke care. Mayo Clin Proc 2004;79(10):1321–1329. 32. Case CS, Mohr JP, Caplan LR. Clinical manifestations of stroke: intracranial hemorrhage. In: Barnett HJM, Mohar JP, Stein BM, et al. eds. Stroke: pathophysiology, diagnosis and management, 2nd ed. New York: Churchill Livingstone, 1992:561. 33. Mohr JP, Hilal SK, Stein BM. Clinical manifestations of stroke: arteriovenous malformations and other vascular anomalies. In: Barnett HJM, Mohar JP, Stein BM, et al. eds. Stroke: pathophysiology, diagnosis and management, 2nd ed. New York: Churchill Livingstone, 1992:659.

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34. Mohr JP. Clincal manifestations of stroke: intracranial aneurysms. In: Barnett HJM, Mohar JP, Stein BM, et al., eds. Stroke: pathophysiology, diagnosis and management, 2nd ed. New York: Churchill Livingstone, 1992:617. 35. Annegers JF, Hauser WA, Coan SP, et al. A population-based study of seizures after traumatic brain injuries. N Engl J Med 1998;338(1):20–24. 36. Shou SN, Kramer RS, Shapiro WR. Neurological and neurosurgical conditions associated with aviation safety: intracranial tumors—panel 2. Arch Neurol 1979;36:739. 37. Deuschl G, Krack P. Tremors: differential diagnosis, neurophysiology, and pharmacology. In: Jankovic J, Tolosa E, eds. Parkinon’s disease and movement disorders. Baltimore: Lippincott Williams & Wilkins, 1998:429. 38. Kapoor WN, Smith M, Miller NL. Upright tilt testing in evaluating syncope: a comprehensive literature review. Am J Med 1994;97:78–88. 39. Kapoor WN, Brant N. Evaluation of syncope by upright tilt testing with isoprot erenol. Ann Droit Int Med 1992;116:358–363. 40. Brooks R, Ruskin JN, Powell AC, et al. Prospective evaluation of dayto-day reproducibility of upright tilt-table testing in unexplained syncope. Am J Cardiol 1993;71:1289–1292. 41. Aronson AE, Auger RG, Bastron JA, et al. Chapter 15:Electroencephalography. In: Mayo clinic examinations in neurology, 5th ed. Philadelphia: WB Saunders, 1981:287. 42. Engel J Jr. Seizures and Epilepsy. Philadelphia: FA Davis, 1989: 313. 43. Ajmone Marsan C, Zivin LS. Factors related to the occurrence of typical paroxysmal abnormalities in the EEG recordings of epileptic patients. Epilepsia 1970;11:361–381. 44. Gumnit RJ. The Epilepsy handbook. The practical management of sezures, 2nd ed. New York: Raven Press, 1995:5. 45. Leppik IE. Contemporary diagnosis and management of the patient with Epilepsy, 6th ed. Newtown: Handbooks in Health Care, 2006:61. 46. Salinsky M, Kanter R, Dasheiff R. Effectiveness of multiple EEG’s in supporting the diagnosis of epilepsy: an operational curve. Epilepsia 1987;28:331–334. 47. Daly DD, Pedley TA. Current practice of clinical electroencephalography, 2nd ed. Philadelphia: Lippincott-Raven, 1997:316. 48. Hopkins RO, Beck CJ, Burnett DL, et al. Prevalence of white matter hyperintensities in a young healthy population. Neuroimaging 2006;16(3):243–251. 49. Takao M, Koto A, Tanahashi N, et al. Pathologic findings of silent hyperintense white matter lesions on MRI. J Neurol Sci 1999;167(2):127–131. 50. Porter A, Gladstone JP, Dodick DW. Migraine and white matter hyperintensities. Curr Pain Headache Rep 2005;9(4):289–293.

RECOMMENDED READINGS Aminoff MJ, ed. Neurology and general medicine, 2nd ed. New York: Churchill Livingstone, 1995. Rowland LP, ed. Merritt’s textbook of neurology, 9th ed. Baltimore: Williams & Wilkins, 1995. Wiebers D, Dale AJD, Kokmen E, et al. eds. Mayo clinic examinations in neurology, 7th ed. St. Louis: Mosby, 1998.

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Aerospace Psychiatry David R. Jones

But let us set before the eyes of the mind a much more lovely spectacle . . . in which people, who while still alive become earthly gods rising on a golden chain toward Heaven . . . who know all arts and sciences . . . —Johann Daniel Major, 1670 (1)

God denied to men the faculty of flight so that they might lead a quiet and tranquil life, for if they knew how to fly they would always be in perpetual danger. —Johann Caramuel Lobkovitz, 1670 (1)

. . . flying is not dangerous, it is interesting. —Richard Bach, 1963 (2)

Aeromedical practitioners (civilian aviation medical examiners and military flight surgeons) select fliers and maintain their physical health in a manner that differs considerably from the conventional practice of clinical medicine. Likewise, aerospace psychiatry affirms normal cognition, emotional stability, coping skills, and behavior as defined in terms of flying safety and effectiveness, thereby differing from the primary concerns of clinical psychiatry with the diagnosis and treatment of mental disorders. Flying is more than a means of transportation. Most writings of early aviators and the physicians who worked with them note that safe and effective flying involves more than simply having the desire and the physical capacity to fly. The terms used to describe the mental, emotional, and psychologic factors involved in aviation have varied considerably over the years, but the existence of these necessary qualities has never been in doubt. Three of the nine chapters in Anderson’s early book on aviation medicine discussed such matters as ‘‘the psychology of aviation,’’ and 406

‘‘the aeroneuroses.’’ ‘‘Nervous breakdowns have been noted since the early days of flying. In fact, they may be classed as an occupational neurosis [in] a comparatively new occupation, namely: aviation’’ (3). Aircraft and their missions have changed since the days of wood, wires, and dope-covered linen, and the pilot population also has changed. Whereas our predecessors supported a homogeneous group of young men and a few young women, now we must consider people of all ages flying in general aviation, commercial aviation, peacetime or combat military aviation, and short- or long-duration space missions. Aeromedical practitioners still seek to select prospective fliers with healthy motivation, adequate innate physical and mental abilities, stable temperaments, and adaptive coping skills, but now we must maintain or enhance these characteristics throughout flying careers of 50 years or more. Fliers writing about aviation may discuss matters that involve what we now call ‘‘human factors’’ (see Chapter 24)

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but they also discuss, in some way or other, the pure joy of flying: the positive emotional factors that form an inescapable and essential part of the reasons that fliers love to fly. No other word will do. Fascination with the idea of flight is as old as the human race. Primal themes include the idea of the air as a living female entity. Air stimulates the imagination because it is invisible, unpredictable, and exists between heaven and earth. Invisible beings with the power of flight seem to inhabit this realm: angels, fairies, sylphs, winged demons, and the like. No religion or mythology fails to discuss or illustrate the existence of such creatures. The very concept of ‘‘up’’ involves becoming closer to heaven, as shown in the writings of St. Augustine, and the spirits of the air could move so speedily that they could appear to predict events (1). Armstrong (4) related the emotional aspects of aviation to a spiritual experience, noting that all religions portray flight as a divine gift. In the oft-quoted words of Magee’s sonnet ‘‘High Flight,’’ the ultimate act of the flier is to ‘‘Put out my hand and touch the face of God’’ (5). Military aviators, a traditionally unemotional group, give each other plaques inscribed with this poem. In short, psychologic factors are intrinsic to aviation. Medical literature, by its nature, tends to discuss things that go wrong. The medical specialty of clinical psychiatry deals with mental disorders: their causes, diagnoses, and treatments, as well as their preventive aspects. Aerospace psychiatry differs from clinical psychiatry in several ways. Stated succinctly, not all mentally normal people are fit to fly, and not all mental disorders necessarily render a pilot unfit to fly. Aerospace psychiatry must deal with positive as well as negative mental health matters, for the absence of positive mental attributes, by no means definable as a mental disorder, may degrade safe and effective flying as surely as the presence of mental disease. Psychiatric disorders in fliers can affect flying safety and effectiveness at subclinical levels that do not warrant formal psychiatric diagnoses in nonfliers. Aerospace psychiatry also involves the system of physical examinations that certifies fliers for specified periods, examinations that include a prediction that the flier will remain mentally fit to fly at least until the next evaluation. In some military and commercial settings, the examiner may also be charged with selecting fliers who will be able to fly for a full career, that is, for 20 years or more, or until retirement age. This long-term requirement stands in stark contrast to the difficulty that clinical psychiatrists face in predicting whether a depressed patient will become suicidal in the next few weeks. Operational aeromedical practitioners make psychiatric decisions about fliers in their offices. These practitioners may have varying levels of psychiatric experience and skill. Aerospace medicine describes the world of the aviator in ways that do not allow for easy translation into psychiatric terms, and so a flight surgeon and a clinical psychiatrist may describe the same phenomenon in quite different ways. Close coordination and cooperation is essential between the practitioners of aerospace medicine and their mental health consultants who may have varying knowledge of, or interest in, the aeromedical aspects of the matter in question.

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Flight surgeons’ decisions about fliers are not based on the usual clinical indications alone, but also on the aeromedical implications. Most psychiatrists would not understand the implications of ‘‘thinking ahead of the aircraft,’’ ‘‘get-homeitis,’’ or ‘‘poor situational awareness’’ without considerable explanation. Only a few physicians have trained and practiced in both fields to the extent that they may make aeromedical judgments about patients suffering from mental disorders without consultation. Need for interdisciplinary cooperation arises in part because some fliers react quite differently to aviation stressors than they do to life stressors. Mental health factors that would be of little concern in everyday life—this defines subclinical—may compromise aviation safety and effectiveness in ways of which a non–aviation-oriented physician, psychologist, or counselor may simply be unaware. Human lives involve infinite circumstances of thought and behavior, which by definition may never all be included in a set of regulations. Therefore, knowing which problems are not compatible with safe and effective flight calls for a mature professional understanding of the principles underlying aeromedical decisions concerning mental health. A textbook that is used by aeromedical practitioners in different countries should point out that cultural differences will affect some of the matters discussed in this chapter (e.g., attitudes toward women pilots or toward the treatment of symptoms of acute stress reactions in combat). In presenting the mental health aspects of selection, health maintenance for safe and effective flying, reactions to stressors of life and of aviation, and other aeromedical topics, we will discuss useful principles rather than explicit answers that may not fit the reader’s circumstances, or that may quickly become obsolete.

SELECTION OF FLIERS Aeromedical mental health standards should pertain to flying safety and effectiveness, or to the health of the flier. Each criterion should be carefully justified because as more standards are used for selection less people can meet them all. Failing to meet a criterion may disqualify a person from employment, and so each standard must meet metastandards of fairness, validity, and equity. Valid standards should address safety, health, dependability, and competence, and the factors examined should be as objectively measurable and reproducible as possible. The ultimate validation of mental health in aviation is the flier’s career-long health, safety, and effectiveness. Researchers studying the effectiveness of various selection techniques have used different outcome criteria: solo flight, graduation from training, accident rates, and the career progression of graduates for up to 5 years. Any comparative assessment of this research must consider these different criteria. Some selection processes seek to identify those who are fully qualified to fly by disqualifying only those who have disorders (select-out), and some seek the best qualified among those who are not disqualified (select-in) (6).

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Mental health standards continue to evolve as the mental health disciplines advance from their subjective historical roots toward objective measurements of mental function (psychologic and neuropsychologic testing), and toward an empirical foundation for classification of mental disorders, as described in the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV) of the American Psychiatric Association (7, (p. xv). Advanced methods of examining the central nervous system [functional magnetic resonance imaging, positron-emission tomography, singleproton emission tomography, and technologically enhanced (quantitative) electroencephalography] offer diagnostic precision, and some may eventually become practical selection tools. Future genetic research may help identify the functional origins of the temperamental qualities of successful aviators. For now, though, most authorities depend on interviews and psychological tests for aeromedical qualification of prospective fliers and leave their operational selection to the intuition and experience of flight instructors. The selection process may be divided into matters involving motivation, aptitude for the job (ability), and sensitivity to self and others (stability) (6, (pp. 100–111).

Motivation to Fly Motivation is the psychic force or energy that moves a person to satisfy a yearning or to achieve a goal. Healthy motivation to fly resembles a motivation for an artistic career or a career in medicine in its combination of emotional (limbic, irrational) and cognitive (cortical, rational) components. Many pilots will say, ‘‘I’ve wanted to fly for as long as I can remember,’’ which is evidence of the deep roots of their motivation. The proportion of emotional and cognitive elements in a specific flier changes with age, experience, and other life factors such as marriage, children, and normal events of life. A flier’s answer to the question ‘‘What do you tell yourself about the dangers of flying?’’ change after a crash, after marriage or the birth of a baby, or simply as the flier ages. Therefore, motivation to fly should be regarded as a dynamic process that may be reassessed when aeromedically necessary. Motivation to fly may represent equilibrium between positive factors (e.g., joy, emotional meaning, and coping skills), and negative factors (e.g., fear, anxiety, and experienced or anticipated danger). The pure emotional joy of flying offsets a healthy fear of its true dangers. The subconscious ‘‘meaning’’ of flying (it represents power, freedom, independence, control, and other basic urges) can also give rise to anxiety if these primal elements are threatened. This may occur if the flier senses a loss of control over life situations (marital or family discord), resulting in a phobic fear of flying (FoF). Finally, the flier’s coping skills, necessary for basic resilience, hardiness, and stress tolerance, may be overcome by the actual dangers of flight as encountered in near collisions, accidents involving oneself or respected friends, or in combat situations where control is impossible (8,9). Some fliers choose to fly not because of an emotional attraction, but because of a more rational attraction (e.g.,

financial rewards, social status, or travel). Because they do not have a strong emotional commitment to flying, these ‘‘rational choice’’ fliers may move on to other careers or activities without much internal struggle (symptoms) when their life circumstances change or when the real dangers of flight exceed their perception of the rewards of flying. A survey by McGlohn et al. (10) contrasted the mix of emotional and rational motivational elements in male and female U.S. Air Force aviators. The reasons most endorsed by the men (45%) emphasized the emotional elements that attracted them to aviation, whereas those most endorsed by the women (34%) emphasized the rational elements. Any assessment of a person’s motivation to fly must deal with basic emotional issues involving ‘‘flying and dying.’’ Flying, a fascinating, dangerous activity, is both loved and feared—loved because of its power, grace, and beauty; feared because of the chance of catastrophe (11). Fliers who value their appearance of rationality and coolness may speak in unemotional terms about aviation matters that in fact have deep emotional roots. Because fliers by inclination and culture tend to downplay (suppress) emotional matters, or to compartmentalize (deny or even repress) them entirely, they may not recognize the strength of these issues in their own lives. Aeromedical practitioners must consider possible emotional factors whenever a flier’s response to a situation does not make sense (is irrational), or involves an inappropriate emotion, or seems disproportionate to the stressor involved. These three factors—irrationality, inappropriateness, and disproportionality—indicate underlying emotional components of aviation-related symptoms. Some fliers have a flawed or pathologic motivation to fly. A need to compete with a fearful father figure through aggressive activity carries with it the unconscious fear of retribution should the effort succeed. Such individuals may become increasingly anxious as they move toward their goal of becoming an aviator. Others may be living out a parent’s own fantasy, or trying to prove that they are not afraid although no one said they were (counterphobic), or seeking risks in search of thrills (high stimulus threshold). A few would-be pilots do not wish to fly for its own sake, but wish to attain the role of pilot to compensate for feelings of inadequacy. Seeing themselves as alienated from others, inept, or weak, they wish to acquire the gregarious, competent, and powerful attributes they perceive to be those of fliers. Such pathologic motivations may underlie significant symptoms or downright dangerous flying behaviors in the absence of diagnosable psychiatric disorders. Weak or flawed motivation, or poor defenses against the real dangers of flying, may be recognized during flight training as ‘‘manifestations of apprehension,’’ or early in an active flying career as ‘‘FoF.’’

Ability to Fly ‘‘Ability’’ involves a flier’s physical, cognitive, autonomic, neurophysiologic, and psychologic traits. These include situational awareness, spatial perception, capacity for mental calculation, suppression of emotional responses during urgent

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situations in favor of analysis and correct action, psychomotor skills (‘‘good hands’’), and alertness to a wide range of sensory inputs, along with the ability to screen out stimuli of no aeronautical importance. No one can excel in all these areas, but safe and effective flight requires a balance of such capabilities; flying requires more than clinical psychiatric normality. Abilities vary, and their assessment is not primarily aeromedical. Flight instructors can identify students with ‘‘good hands’’ during flight training, a crucial part of the select-in process that complements the medical process. They appraise the in vivo cockpit performance of applicants in matters involving intelligence, perception, attention, interpretation, and the speed and quality of decisions, based on variable sensory stimuli under flight training stress. These attributes are elemental to the ability to perform the mental and physical processes necessary for safe flight. Aeromedical specialists and aviation psychologists have worked for decades to isolate these specific abilities and this process will undoubtedly continue for decades to come. Recent advances in flight simulator technology are challenging the conventional wisdom that only experience in actual flight can teach a person to fly. However, even the most sophisticated devices cannot duplicate fully the physical sensations and sensory inputs of actual flight (e.g., gravitational forces, pressure changes, total range of sound and vibration), nor can they overcome the student’s underlying knowledge that a mistake in simulated flight may be embarrassing, but will not result in sudden death. This surety means that the student does not experience the full effect of the powerful emotional, autonomic, and hormonal stimuli that may occur when the same situation occurs in a real aircraft, just as simulated combat training cannot entirely prepare anyone for the real thing (12).

Stability ‘‘Stability’’ involves personality, temperament, and interpersonal relationships, including attitude toward authority. Even a lone private pilot must decide when and where to fly, must share airways, and must adhere to flying regulations and instructions. The aviator’s general attitude toward flying involves a way of thinking about weather, time of day or night, fatigue, circadian rhythm, readiness to deal with sudden inflight emergencies, and a host of other factors well known to pilots. Collectively, these are part of what the aviation community calls ‘‘human factors.’’ A pilot’s mistake in such matters can be as suddenly lethal as a midair collision, and skilled pilots have died from such avoidable choices as knowingly flying into thunderstorms or failing to perform complete preflight walk-around inspections because they were in a hurry. Consideration of aviator stability includes an appraisal of personality (temperament). Probably no occupation has attracted as many studies of the personalities of its participants as has aviation. Beaven mentioned control of the imagination, patience, and a strong motivation to fly as important during World War I (13). Fine and Hartman

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emphasized above-average intelligence, a matter-of-fact view of life, and a preference for action over introspection; this latter characteristic explains why some fliers tend to act out their interpersonal frustrations rather than considering possible solutions (14). A study of 105 successful male military pilots noted their self-confidence, desire for challenge and success, and strong identification with their fathers. They tended to be eldest sons, to make life choices on a consciously rational basis, and to take risks only when their assessment of the odds led to a high chance of the desired outcome. They made friends easily, but avoided dependency and thereby maintained interpersonal distance (15). Christy described the balance between factors such as rigidity and flexibility, and the need for maturity, good motivation, and self-confidence, qualities that likely would assure success in any field of endeavor (16). Modern research into the temperaments of successful aviators uses a more disciplined terminology. It does not depend on the clinical psychiatric literature for its vocabulary, nor does it follow the older aeromedical literature practice of describing fliers’ personalities by using everyday words rather than strictly defined and measurable terms. Helmreich et al., in their research into crew resource management (CRM), have identified two personality dimensions that affect aircrew performance: instrumentality, the work orientation, mastery of tasks, and desire to achieve; and expressivity, which includes interpersonal communications and sensitivity (17). They used interviews, questionnaires, and video techniques that allowed careful analysis by investigators, instructors, and the aircrew themselves. This research has produced information about effective and ineffective aviator personalities, although the investigators have not presented their results in clinical terms. Fliers may manifest instrumentality or expressivity either positively or negatively, and both factors are important in cockpit transactions. The CRM approach has identified three categories of aviators. The first has positive elements in both dimensions. Positive instrumentality means a strong work orientation, drive to achieve, and drive to master the task. Positive expressivity includes low competitiveness and low verbal aggression. This combination seems the best for multicrew cockpits. During CRM training, such crews have the highest scores on coordination and communication skills, and best manifest the desirable attitude that responsibility rests with the entire crew rather than with the leader. They develop the most judgment and insight about their own reactions to stressors. Crews demonstrating high instrumentality and low expressivity have the positive instrumentality characteristics of the first group, but are competitive and verbally aggressive (negative expressivity), are less skilled in communication and coordination, learn little about command responsibility, and show only modest recognition of stressor effects. A third group of aviators has both low instrumentality and low expressivity. This group does poorest in communication and coordination, actually regresses in appreciation of collective responsibility during training, and shows little recognition of personal stressor effects (17).

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Helmreich’s research uses the methods of industrial or occupational psychology. The utility of the CRM concept has led to its application to other fields, such as the interactions of nuclear reactor control teams and the relationships between surgeons and anesthesiologists in operating rooms.

Selection Process Mental health evaluations of aviators differ from usual clinical psychiatric interviews. Aeromedical examiners seek not only to affirm mental health in the ordinary sense, but also to determine when a normal person has the motivation, ability, stability, maturity, attentiveness, perception, anticipation, and judgment to make good decisions before and during a flight, and the hardiness and resilience to endure under prolonged stressors. The aeromedical practitioners responsible for physical examinations and the authorities that receive and evaluate the reports of these examinations must assess the possibility of aeromedically significant degradation of fliers during the interval until the next evaluation. In occupational selection of professional pilots, examiners must consider future fitness for a flying career of 20 years or more. One approach to gauging the mental health of both prospective and trained aviators requires examiners to use a semistructured interview or a checklist. Flight surgeons perform formal assessments of adaptability in the U.S. Navy (Aeronautical Adaptability) (18,19) and U.S. Air Force (Adaptability Rating for Military Aviation) (20). The results vary in quality and usefulness because examiners’ psychiatric interviewing and observational skills differ, as well as their time for and personal interest in such evaluations. Although any practicing physician may recognize full-blown psychiatric disorders, lesser symptoms can be difficult to detect, especially if the flier conceals the difficulties (suppression, lying) or is unaware of them (denial, repression). The little formal research on this examination technique has not confirmed its predictive value (20). Difficulties in this endeavor include subtleties of the interview process (e.g., reverse malingering or ‘‘faking good,’’ resistances, experience of the examiner, the transference/countertransference interplay) and problems of recognizing significant symptoms and obtaining adequate and timely consultations when such symptoms are present (12). Newly trained aeromedical practitioners soon develop professional and personal instincts about aviators, recognizing the bearing and behaviors of healthy fliers and forming useful preliminary impressions of their mental health. Some clues may be available as the examination begins: the reputation of the applicant in the community, or an examinee’s interaction with office staff. Flying candidates or experienced aviators who have mental health problems may behave differently with office staff than with the examiner, and so the staff should report any behavioral problems or eccentricities to the aeromedical practitioner. Many examinations require that the examinee fills out a form before seeing the examiner. The examinee may mark carelessly, or omit, some answers. Examiners should obtain the correct or missing data and ask why the flier made

this particular mistake; because a few fliers will not wish to lie directly, but will try to avoid reporting information they regard as negative. If the applicant does not live or work locally, the examiner may ask why he or she came so far; some will ‘‘shop around’’ for lax examiners, or will repeat examinations to learn how to conceal disqualifying information. Examiners also should inquire carefully into any history of consultation with mental health professionals or paraprofessionals (lay counselors, company support programs) and ask about nonprescription medications, herbal remedies, and dietary supplements. Such information may be aeromedically significant because of the nature of these remedies, or because of the symptoms for which the pilot feels they are necessary. Be alert for illogical explanations about medical history or findings. If a flier’s explanation does not seem reasonable, ask for more details. If an examiner cannot understand a flier’s earnest efforts at explanation, benign possibilities include misunderstandings, communicating in the flier’s second language, educational deficiencies, cultural differences, or limited intelligence. However, the difficulty may be due to a neurologic or psychiatric problem. Behaviors that caused body scars may represent patterns of personal recklessness. The scalp and skull should be palpated for evidence of head injury because these may have involved loss of consciousness or amnesia. Other pertinent physical findings bearing on mental status include unusual conduct, dress, grooming, tattoos or body piercings that suggest sociopathy, slash scars on wrists (possible suicide attempts), or stigmata of substance abuse such as odor of alcohol, needle tracks, or nasal septal scarring or perforations. The physician should talk with applicants before, during, and after the physical examination, inquiring about home, work, education, military experience, and flying activities. Again, examiners should trust their judgment that something may be amiss psychologically if they feel uneasy about the examinee. At the end of the evaluation, the aeromedical practitioner should have enough information to decide whether a mental health disorder might be present, and whether outside medical data ought to be obtained. If anything raises clinical questions about the examinee’s mental status, or even if the examiner feels uncomfortable without knowing exactly why, a brief mental status evaluation (MSE) must be performed, using some or all of the items in Table 17-1. Note that this MSE extends beyond items considered in clinical ‘‘miniMSEs’’ that are limited to evaluating the sensorium rather than assessing wider aspects of cortical function. Examiners who detect possible problems should defer certification and obtain formal mental health consultation to delineate these concerns more clearly. The certifying authority may have protocols to guide this process.

Selection for Space Flight Evaluating the mental health and temperaments of individuals seeking to become astronauts includes several factors not considered for other types of flying. The United States National Aeronautics and Space Administration’s (NASA’s)

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Formal Mental Status Examination (‘‘AMSIT’’) Appearance, behavior, and speech Physical appearance: Apparent age, sex, and other identifying features. Appearance of being physically ill or in distress; and a careful description of the patient’s dress and behavior. Manner of relating to examiner: placating, negativistic, seductive; motivation to work with examiner. Psychomotor activity: increased or decreased, including jumpiness, jiggling, tapping, looking at watch, and so on. Is the person hyperactive or lethargic? Behavioral evidence of emotion: tremulousness, perspiration, tears, clenched fist, turned-down mouth, wrinkled brow, and so on. Repetitious activities: mannerisms, gestures, stereotypy, ‘‘waxy flexibility,’’ and compulsive performance of repetitious acts. Disturbance of attention: distractibility and self-absorption. Speech: Description—volume, rate (pressured or slowed), clarity, and spontaneity; Disturbances—mutism, word salad, perseveration, echolalia, affectation, neologisms, and clang speech Mood and affect (Note: ‘‘Mood is to affect as climate is to weather.’’) Mood: use adjectives—mild (it’s there), moderate (it needs treatment), or severe (it needs treatment today). Consider depression, elation, or other sustained emotions such as anger, fear, or anxiety. Affect: its range, intensity, lability, and appropriateness to immediate thought. To describe a normal, stable emotional status, say something like, ‘‘The examinee’s mood is euthymic. Affect is unremarkable in range, intensity, and stability, and is appropriate to material being discussed.’’ Sensorium Orientation: for time, place, and situation. Memory: immediate (digits recall), recent (three items for 10 min, current events), and remote (history). Calculating ability: serial 7s, 11 times 13 out loud (valid only if patient is adequately educated). Concentration: spell world backward, then arrange its letters alphabetically; repeat with earth. Intellectual function Estimate current level of function as above average, average, or below average based on general fund of information, vocabulary, and complexity of concepts. Do not confuse intelligence with education. Can the examinee handle abstract ideas, reason by analogy, ‘‘make the connection’’ in conversation? Is the examinee about as smart as the examiner? Thought Coherence: clear thoughts may be expressed incoherently. Logic: even clear, grammatical speech may express illogical thoughts. Goal directedness (has a point and makes it): tangential or circumstantial thought. Disturbance of attention: distractibility (interrupts own sentences), self-absorption. Associations: loose associations, blocking of obvious ideas or connections, and flight of ideas Perceptions: hallucinations (false perceptions), illusions, depersonalization, and distortion of body image. Delusions: false interpretations of real situations. Other content: noteworthy memories, thoughts, and feelings; suicidal or homicidal intent. Judgment: formal (specific set-piece situations such as ‘‘mailing a letter you find on the street’’) and social (how examinee behaves with examiner, how examinee ‘‘reads’’ other people—as predictable or unpredictable, reasonable or irrational, comfortable or threatening). Abstracting ability: ask pilot to define similarities/differences between tree–bush, child–midget, king–president, character–personality. This is more reliable than interpreting proverbs (stitch in time, bird in the hand). Insight: understanding of any personal dysfunction affecting self or others and its need for treatment; insight is lacking if there is an unacknowledged problem, superficial if it is only acknowledged (‘‘It is a problem’’), moderate if it is personalized (‘‘I have a problem’’), and profound if the person takes responsibility (‘‘It’s my problem, and it’s up to me to fix it’’) AMSIT, appearance, mood, sensorium, intelligence, and thought. (This version of the AMSIT is adapted and reprinted from a formulation by Fuller DS. In: Leon RL. Psychiatric interviewing: a primer, 2nd ed. New York: Elsevier/North-Holland, 1982:75–77; with permission.)

intensely competitive biannual selection process may involve more than 3,000 initial applicants for 20 openings. The primary screening involves record reviews, but the final selection requires personal interviews and psychological testing. Almost any past or present psychiatric diagnosis will be grounds for disqualification, the binding select-out process. Mental health select-in is by no means binding because other medical and occupational standards will be applied to the applicants. However, the selection committee may consider identifiable

positive personal qualities in its deliberations. Applicants are considered not only on the basis of their success in earth-bound occupations, but also in terms of their possible resilience or vulnerability to environmental stressors, prolonged isolation in small groups, and their interpersonal adaptive skills in groups of mixed gender, culture, ethnicity, occupation, and authority. Examiners must consider whether persons are self-sufficient or seem to require high personal maintenance from associates and authorities.

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Because astronauts may undergo expensive training and service status for many years before actually flying in space, hereditary factors must also be considered in terms of expected future mental health. Some of these psychiatric and psychological factors go well beyond the usual definition of relative mental health: simultaneous success in work, personal relationships, and creativity, with the capacity to handle conflicts between instincts, conscience, important other people, and reality with maturity and flexibility (21, p. 127). High standards of mental health for space crewmembers may seem intuitive, but are difficult to apply fairly and within legal and ethical limits. Although evidence-based standards would be ideal, clinical psychiatric literature, which usually concerns mentally ill individuals, seldom provides explicit data applicable to the early and subclinical conditions that space crew examiners must consider. NASA criteria generally follow the diagnostic formulations of DSM-IV (7), adding specific considerations for ‘‘traits’’ and subclinical manifestations. These criteria have been developed through a series of NASA-sponsored interdisciplinary meetings of operational flight surgeons, astronaut flight surgeons, aeromedical and clinical psychiatrists and psychologists, epidemiologists, and psychological testing experts. During the selection process, psychological tests normed for the astronaut population add some objective data to the interviews, and all decisions are peer reviewed for possible individual bias. As with aircrew, anxiety disorders, mood disorders, and undesirable personality traits are the most common reasons for disqualification (22). Those responsible for developing and justifying selection and retention criteria have studied space-analogous circumstances such as Antarctic overwinter stays, nuclear submarine cruises, survival situations, and historic expeditions (6). The subject of space crew mental fitness and collective interactions has been examined in the literature mainly, although crew questionnaires obtained before and after missions [for a summary of these data, see Kanas and Caldwell (23)]. Policies of the various space agencies, small size of space crew populations, intense public scrutiny, and difficulty in maintaining individual anonymity make case reports difficult. Still, with continued attention to the subject, and especially with the development of private individual onboard computerized questionnaires, data should accumulate over the next few years. As mission lengths increase and crews become even more heterogeneous, such data will be essential to mission safety and effectiveness and to the mental health of individual crewmembers. Selection involves predictions of continuing health and especially of mental health, and is a difficult business indeed. Any system of aeromedical selection and certification depends not only on the examiners and the formal criteria, but also on the intelligence, insight, and integrity of the fliers to be forthcoming about medical matters, and to recognize and acknowledge when they are not fit to fly.

MENTAL HEALTH STANDARDS, MAINTENANCE, AND WAIVERS Formal mental health standards for aviators vary with the type of aviation involved and the certifying authority. In general, the most rigorous standards apply to civil air transport pilots who may command airliners carrying hundreds of passengers, to astronauts and cosmonauts, and to military pilots chosen to fly high-performance aircraft for a career of 20 years or more and who may have access to weapons of mass destruction. The variability of mental health standards makes it difficult to discuss them in more than general terms, and examiners must familiarize themselves with whatever regulations apply to the fliers they evaluate. Aeromedical practitioners should maintain a reasonable level of awareness of mental disorders (clinical suspicion) and request competent consultation when they suspect that pilots have mental health problems. Zimmerman’s brief but excellent book lists specific questions useful to the nonpsychiatrist in identifying specific psychiatric disorders (24). A brief clinical assessment may help the aeromedical practitioner to reach primary conclusions about the mental health of an applicant and to decide if further consultation is necessary. Personality disorders may pose a particular challenge (18). The section that follows briefly presents the major categories of mental disorders and considers their aeromedical implications. The reader is referred to DSM-IV (7) and to current psychiatric texts for detailed information about specific mental disorders. Any psychiatric disorder that the aeromedical examiner feels may degrade aviation safety should be cause for deferral of a medical certificate, subject to review by higher aeromedical authorities.

Specific Mental Disorders Psychotic Disorders Psychotic disorders involve gross impairment of the ability to perceive reality. A psychotic person may create a personal interpretation of the surrounding world even in the face of contrary evidence that would persuade a nonpsychotic person. Such disorders characteristically involve delusions (firmly held false beliefs about real situations), hallucinations (false sensory perceptions), illusions (misinterpretation of real sensory stimuli), depersonalization (loss of perception of one’s own reality), loose associations (illogically connected ideas), or disorganized, bizarre behavior or speech. All present or previous psychotic disorders should disqualify a person from being an aviator. Waivers or special issuances may be granted when the cause is unequivocally identified as one that was temporary, has ceased, and should never recur (e.g., a past dementia due to toxins, infections, or metabolic problems). Rarely, a mentally healthy aviator undergoing an intensely stressful situation will experience a brief reactive psychosis that clears completely and thereby meets criteria for possible waiver. Positive identification of the cause, along with sound psychiatric treatment, full recovery, and a carefully observed period of subsequent

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psychiatric normality may allow for consideration of return to flying. Aeromedical judgments in such cases should be conservative, regardless of how sympathetic one is to the desire of the flier to fly again.

Bipolar Affective Disorders Bipolar affective disorders (BADs), formerly known as manic depressive disorders, may take several forms. Psychotic manic episodes are likely to recur despite medication, and so should lead to permanent disqualification. Nonpsychotic BADs have a high recurrence rate and may progress to include psychotic episodes, and so most regulatory authorities regard BAD as intrinsically disqualifying for fliers. Both psychotic and nonpsychotic BAD may respond to medications such as lithium carbonate, anticonvulsants, and mood stabilizers that are themselves a basis for disqualification. Current clinical psychiatric practice includes long-term prophylactic use of such medications after a manic or depressive BAD episode has cleared. This practice leads to difficult choices between leaving such asymptomatic fliers grounded on medication or discontinuing the medication to return the fliers to the cockpit, thereby exposing them to increased risk of recurrence and possible drug resistance. If a flier with a nonpsychotic BAD is considered for waiver, the flier, treating psychiatrist, and aeromedical practitioner should jointly make careful and informed decisions. A company physician may be consulted if the flier is a professional pilot. The certifying authority must approve any decision to return the aviator to flying. Depressive Disorders Depressive disorders may present with somatic or emotional symptoms, or with both. Because aviators tend by nature to pay less attention to their internal emotional climate and more to their physical symptoms, they are likely to complain primarily about the way they feel physically, rather than about emotional distress. Somatic symptoms include changes in sleep patterns such as difficulty falling asleep, difficulty staying asleep, restless sleep leading to early morning fatigue, or too much sleeping (hypersomnia). Appetite may increase or decrease, perhaps with weight change, constipation, or diarrhea. The flier may complain of loss of usual concentration and memory, and of headaches or other minor but annoying aches and pains. Emotional symptoms include apathetic loss of interest in usual activities, anhedonia (loss of joy in life), visible slowing (psychomotor retardation) or agitation, distraction, and indecision. The mood may be depressed most of the time, with inappropriate tearfulness, feelings of worthlessness or undeserved guilt, self-reproach, desire to flee from life situations, or deathrelated ideas that may represent abstract suicidal ideation or may be frankly self-destructive, even including a specific plan (25). Few aeromedical practitioners would miss the diagnosis if the flier listed the symptoms as openly as given in preceding text, but some of these signs and symptoms may develop slowly over several weeks or months and not be as clear. Some

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physicians identify so closely with ‘‘their’’ fliers that they do not wish to label a disorder as ‘‘depression,’’ perhaps fearing that they will stigmatize a flier to whom they give a psychiatric diagnosis. Some mental health professionals enter into this state of affairs, even in formal consultation, minimizing the symptoms of depressive disorders as being due to external circumstances. Incorrect lesser diagnoses may be given, at times with the stated aim of ‘‘not hurting the pilot’s flying career,’’ or ‘‘not taking away the only pleasure left, flying.’’ Although this is unfortunate from the ethical point of view, it may have other and more serious consequences. Neither the formal literature nor insurance companies recognize flying as a safe or effective form of psychotherapy. An underdiagnosed disorder also may be undertreated. If a major depression is termed an adjustment disorder, appropriate medications may not be used. Use of antianxiety medications to treat depression may make the depression worse. Self-medication with alcohol may compromise both flying safety and the pilot’s health. A therapeutic course of any antidepressant medication disqualifies an aviator from flying until the condition requiring its use has been alleviated, the medication and its active metabolites have been cleared from the body (approximately five times the biologic half-life of the medication and its psychoactive metabolites), and the flier has remained off medications and symptom-free for 6 months. Proper selection and use of antidepressant medications is a changing field of study, and aeromedical practitioners should follow the literature. Whatever medication is prescribed for a patient must be used properly, with a careful consideration of target symptoms, therapeutic goals, adequate doses, side effects, drug interactions, and previously agreedupon indications for completion and discontinuation of treatment. At this time the presence of depressive disorders requiring current use of medications is disqualifying for medical certification, as is the actual use of psychoactive medications—either the diagnosis or the treatment is disqualifying. Depressions are treatable disorders, and a flier who has been treated, has recovered, has been tapered off medications, and has been symptom-free off medications for approximately 6 months may resume flight privileges with proper authorization. In the United States, the regulations of the Federal Aviation Administration (FAA), NASA, and the three armed services forbid aircrew to fly while taking psychoactive medications. Aeromedical practitioners who knowingly or tacitly allow fliers to fly on such medications do so at their own risk, ethically and legally. These physicians, who overidentify with their depressed fliers, should avoid sympathetic but misguided underdiagnosis and undertreatment. Aeromedical practitioners should also follow the aeromedical literature on this dynamic issue because some modification of official policies may occur in the future (see the discussion of Psychoactive Medications later). Depressive disorders that do not require treatment with medication may not be disqualifying, depending on the nature and intensity of symptoms, the reaction of the flier,

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and his or her insight into the condition. Experienced examiners or flight surgeons should individually evaluate such aviators in consultation with mental health consultants.

Substance Abuse and Dependence Substance abuse and dependence are grounds for disqualification. Medical and administrative policies vary considerably in this complex field. In general, examiners who deal with such patients should base decisions on objective evidence rather than on the unsupported word of drug or alcohol abusers. Aeromedical practitioners must be careful to identify persons with personality disorders among those who abuse alcohol or drugs because personality disorders are themselves a reason for disqualification (Chapter 11 discusses rehabilitation programs for substance abusers). Neuroses According to classic psychoanalytic theory, neuroses represent unconscious anxiety expressed through symptoms that allow the person to assuage the anxiety indirectly and symbolically. The technologic advances that have supported biologically based psychiatry, and the use of the scientific method to test etiologic hypotheses, allow for some alternative explanations that involve the neurochemistry of anatomic pathways. Genetic studies hold some promise for future prognostic accuracy because the fact that medications relieve such disorders suggests the role of biochemical or metabolic factors. The current American Psychiatric Association nomenclature has eliminated the classic term neurosis and has dispersed its diagnoses among four headings: Mood Disorders, Anxiety Disorders, Somatoform Disorders, and Dissociative Disorders (7, pp. 20–21). The ‘‘neurotic’’ forms of mood disorders include some clinical depressions, as discussed in preceding text. Anxiety disorders include phobias, panic attacks, obsessive–compulsive disorder, acute and posttraumatic stress disorders (PTSDs), and generalized anxiety disorder. Somatoform disorders include hysterical or conversion disorders, hypochondriasis, and some pain disorders. Dissociative disorders include dissociative identity disorder (multiple personalities), fugue, amnesia, and similar conditions. All of these disorders should disqualify the flier, although a few exceptions may be granted depending on the nature and severity of symptoms. Mental Symptoms due to a General Medical Condition Mental symptoms due to a general medical condition is the current expression for a condition formerly termed an organic mental disorder. This category of disorder distinguishes mental disorders caused by underlying medical conditions from mental disorders induced by external substances and mental disorders that have no specified cause. The underlying medical diseases generally lead to permanent disqualification unless they are reversible and not likely to occur again (e.g., delirium or dementia from acute metabolic or infectious processes).

Adjustment Disorders Adjustment disorders may require temporary disqualification until the conditions resolve. DSM-IV (7, pp. 623–624) names discrete adjustment disorders with anxious mood, with depressed mood, with disturbance of conduct, with physical complaints, with withdrawal, with work inhibition, and with mixed features. Adjustment disorders occur within 3 months of an identifiable external stressor that may be single, multiple, or recurrent, and may be intermittent or continuous. Stressors may be associated with the marital or the parental family, with flying, with social relationships, with job relationships, with physical illnesses, or with religious, legal, financial, or similar concerns. The severity of the disorder may be disproportionate to the severity of the stressor because personal vulnerabilities and other current stressors may vary as well. Therefore, a stressor that barely affects one person may disable another. In an adjustment disorder, counterproductive or maladaptive emotions or behaviors impair function in occupational, scholastic, social, or personal relationships beyond the normal or expected response to the stressor. Symptoms should abate within 6 months of the stressor or its consequences have subsided. If the stressor continues, the disorder may end when the person attains a more effective and less symptomatic level of adaptation. The ability to handle an aircraft well under difficult conditions of flight does not necessarily indicate an equal ability to deal with all life stressors. Although successful fliers must be able to deal with the specific stressors of flight, this ability does not make them uniquely able to deal with stressors arising from family, interpersonal, or job situations. Marital or relational stressors are the most common sources of difficulty for fliers, followed by interpersonal job-related stressors and career stressors. The afflicted fliers may not be aware of the connection between their stressors and their symptoms. Adjustment disorders are unique to an individual’s present situation, rather than being part of a lifelong pattern that would indicate a personality disorder. If symptoms last longer than 6 months, the diagnosis must be reclassified (e.g., as a depressive disorder). Adjustment disorders associated with substance abuse or dependence must be primarily considered under regulations or administrative procedures concerned with that abuse or dependence, rather than with the adjustment disorder (see Chapter 11). The clinical experience of veteran aeromedical practitioners confirms the wisdom of this policy. Fliers with adjustment disorders may experience nonproductive, persistent fretting about some problem, thinking about distressing things while flying (daydreaming), or obsessively worrying and becoming distracted in the cockpit. They may lose their usual sense of humor (one of the best coping skills). They may become irritable, have outbursts of anger, use more alcohol, or engage in uncharacteristically reckless behavior. Their upsetting thoughts may lead to a sleep disturbance, to feelings of being trapped by the problem, to preoccupation with otherwise minor physical complaints, and even to an FoF, overt or barely disguised.

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These symptoms combine elements of depression, anxiety, and behavioral ‘‘acting-out’’ of distress. Some may be accentuations of a specific flier’s usual personality traits, whereas others may represent a considerable departure from the flier’s norm. When stressors cause such symptoms in a flier who is basically mentally healthy, the genesis of the problem must be clarified. A brief course of medications may be helpful in alleviating acute distress, but such medications will preclude flying. Counseling or formal ‘‘talk therapy’’ may provide insight into the nature of the problem and how better to cope with it. Once fliers understand where their problems lie, most are willing and adept at doing something about them, and aeromedically oriented mental health therapists find such fliers to be motivated, responsive patients. The fliers may require medications for acute symptom relief, but such medications may be discontinued as the pilots improve their life situations, and therefore time lost from flying is usually minimal.

Personality Disorders and Traits Personality disorders may be particularly worrisome because their resultant behaviors in aircrew may require administrative as well as aeromedical action. Any flier whose personality disorder manifests itself through repeated overt acts should receive mandatory medical disqualification. Personality itself (temperament) represents an individual’s conscious and unconscious behavioral patterns and tendencies—the distinctive way he or she behaves in the environment. An individual’s personality derives from genetic, biologic, autonomic, and physiologic attributes, shaped by environmental influences as they are registered, interpreted, stored, and integrated by the central nervous system. Although personality patterns seem to be inborn, childhood influences help develop the brain itself and are therefore crucial to the developing personality. Personality traits are pervasive patterns of feeling, thinking, and behaving that may be appropriate (not distressing to self or others) under most conditions. DSM-IV states, ‘‘Only when personality traits are inflexible and maladaptive and cause either significant functional impairment or subjective distress do they constitute Personality Disorders’’ (7, p. 630). Many people have a few such traits that do not reach the degree of presence or intensity that make them clinically significant (i.e., true disorders). Reactions to environmental or (particularly) interpersonal stress may temporarily accentuate these traits so that they resemble personality disorders, rather than adjustment disorders. Careful history of the time course of the symptoms will allow an accurate diagnosis. DSM-IV describes the diagnostic criteria for ten personality disorders (7, pp. 629–673): paranoid, schizoid, and schizotypal (cluster A); antisocial, borderline histrionic, and narcissistic (cluster B); and avoidant, dependent, and obsessive-compulsive (cluster C). Each has a series of defining symptoms presented in a manner similar to those paraphrased here for antisocial personality disorder. The diagnosis of antisocial personality disorder (older than 15 years) derives from a pervasive pattern of disregard

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for and violation of the rights of others, as indicated by at least three of the following (7) (p. 649): • Would not conform to social norms; commits repeated antisocial or illegal acts • Deceitful: lies, cheats, cons, uses aliases • Fails to plan ahead; is impulsive • Is irritable and aggressive; gets involved in physical fights or assaults • Is reckless concerning safety of self or others • Is irresponsible; does not sustain consistent work or finances • Has no remorse or concern about hurting or stealing from others If a pilot has a personality disorder, it is likely to be antisocial, narcissistic, obsessive-compulsive, or paranoid. Making aeromedical decisions about the fitness to fly of persons with personality disorders may be so difficult as to be almost pathognomonic. The following pointers may help in the process. Medical authorities should endeavor to base a diagnosis of aeromedically significant personality disorder on solid documentation, whether from the aviation milieu or the flier’s outside life. This may be the only way to document or assess the ‘‘overt acts’’ referred to in Federal Air Regulation 67 (26). Psychological tests may be helpful, but are usually not definitive (i.e., they are more sensitive than specific). Formal interpretation of the tests must be normed against aviators, not the general public. When the flier offers complex sets of explanations for a series of improbable life events that have led to medical evaluation, consider a personality disorder as a possible underlying etiology. This diagnosis is especially likely if the flier appears to be one of the nicest people one has ever met, yet claims to be unjustly accused of several somewhat unlikely misdeeds. The aviator may be inappropriately antagonistic or even litigious about an unwanted decision. Treatment of personality disorders is difficult, if not impossible. The aviator may not have experienced any distress, and may even be proud of his or her behavior, therefore seeing no particular need to change. The flier sees the problem as due to others, not to self, and expects the others to change. If the condition is mild (traits), reduction of life stressors and the acquisition of some insight may alleviate the problem, at least in the aviation context. If the condition is serious, then the mental health consultant, the aeromedical authorities, and the appropriate administrative body should collaborate in making the decision. Consultants and aeromedical practitioners must be familiar with the applicable regulations and aeromedical decision factors. It may be useful to point out to the aviator that if a medical cause is not found, the offending acts may lead to administrative termination from aviation-related activities by an employer or by the FAA. Quite possibly the flier may be uncooperative, feeling that any medical diagnosis will be undesirable. Such a question as, ‘‘Do you realize that if

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we find you medically qualified to fly, you’ll be fired (or decertified) for what you did?’’ may make the aeromedical practitioner’s job a bit easier by enlisting the cooperation of the flier in gathering specific information about the events in question. Whether encountered in the setting of the military, in airlines, in corporate flying, or in general aviation, such problems are usually so complex as to make their way up to higher levels of decision than the office-level flight surgeon or aviation medical examiner. The most difficult issue may be whether the decision itself is basically medical (which may entitle the flier to sick leave, treatment, disability benefits, etc.) or administrative (which may involve disciplinary or even legal action, or loss of employment) (18,27). One should remember the basic issue, ‘‘Is this pilot safe to fly?’’ If the behavior pattern in question could affect flight safety, the individual should not fly, regardless of whether the problem is defined as medical or administrative in nature. For example, the nature of the overt acts that led to the evaluation may demonstrate an ongoing lack of respect for authority, which would certainly be significant in the regulated world of aviation. If these aeromedically significant acts stem from a personality disorder, the disorder should be the basis for medical decertification until successfully treated. The difficulty of successfully treating some personality disorders is well known. Should treatment be competently accomplished and objectively documented, the recertification process may be initiated.

Maintenance of Mental Health (Mental Hygiene) General aeromedical concerns include maintenance of health, with particular interest in any disorders that fliers acquire after their selection that could degrade their abilities to function safely or effectively as aircrew members. When such disorders are diagnosed, military fliers are grounded by the proper authority, and civilian pilots may ground themselves or be grounded by the FAA or by their commercial employers. When one considers how such general aeromedical requirements apply to conditions involving mental health, several new elements appear. ‘‘Mental health’’ is relative rather than absolute. ‘‘The best indices of mental health are simultaneous success at working, loving and creating, with the capacity for mature and flexible resolution of conflicts between instincts, conscience, important other people, and reality’’ (21) (p. 127). Mental health therefore involves such unmeasurable factors as personal happiness, the ability to function in many areas of life, and the effect of one person’s actions on others (both close associates and society in general). Some of these factors have an obvious bearing on fitness to fly (suicidal ideas), but others are more difficult to assess (explosive temper). As with medical conditions, psychiatric symptoms may be aeromedically significant before they are clinically significant. For example, a pilot may be distracted in the cockpit by a family problem, thereby not attending to a change in a cockpit

instrument or otherwise not attending to flying conditions. Although these symptoms may not reach the level of a clinical adjustment or anxiety disorder, they may diminish situational awareness and performance, thereby degrading flight safety. One might reasonably expect the flier to recognize the occurrence or recurrence of distressing somatic symptoms. However, some mental conditions affect introspection, insight, judgment, or cognitive function, so self-report may not be entirely dependable, even in pilots of the highest character. This aspect of mental illness mandates disqualification of any pilot with BAD or with a psychotic disorder. Fliers may receive secondary gain from symptoms. In classic psychiatric terms, the primary gain of psychological defense mechanisms is to provide relief from internal conflicts and their attendant anxiety. The secondary gain is that the symptoms may attract ‘‘personal attention and service, monetary gains, disability benefits, and release from unpleasant responsibilities’’ (21) (pp. 166, 188). For example, a male pilot might receive compensation for his phobic FoF for several years. Free of distress in his daily life, he works at another job. He does not pursue psychotherapy for his FoF because he feels well. If he has to return to the cockpit his fears are activated, his symptoms recur, and he becomes disabled once more because of (a) having to return to flying (negating the primary gain from his symptoms) and (b) losing his disability pay (negating the secondary gain). Treatment of such a complex interaction of psychiatric and occupational factors requires more than just prescribing medication. A cognitive-behavioral or psychodynamic approach (talk therapy) may be effective if the flier is willing to form a therapeutic alliance with a therapist, but is unlikely to succeed if the flier does not wish to participate and cooperate in the effort to return to flying activities.

Waiving Psychiatric Disqualification for Flying An individual aviator who has had a mental disorder may receive a waiver or special issuance as an exception to general mental health standards. This process may be undertaken when that flier’s mental disorder is no longer present, or has subsided so that it does not endanger either the flying safety or the effectiveness of the flier, and is unlikely to recur. Although many fliers believe that any psychiatric disorder will end their flying days, most such disorders are waived; 65% of U.S. Air Force fliers hospitalized for psychiatric disorders were returned to flying status (RTFS) within 2 years, and the proportion of fliers RTFS among those with psychiatric disorders who were not hospitalized was even greater (28). Even self-destructive actions do not mandate the end of a flying career; aeromedical authorities ultimately returned to their cockpits 11 of 14 fliers (79%) referred for aeromedical consultation after the successful treatment of the conditions leading to their suicide attempts (29).

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Decision Criteria for Waivers Waiving mental health disorders in an individual flier requires a more detailed and extensive history than that usually given in a ‘‘regular’’ clinical psychiatry consultation, as well as psychological testing with aeromedically sophisticated interpretation. The aeromedical practitioner must judge the certainty of the mental health diagnosis, its probable future course, the options for prophylaxis, the dependability of the flier’s judgment and insight, and the chance of recurrences. Statistical data about the condition must also be analyzed to extract the kind of information necessary for aeromedical decision making. Family information must be considered, including the level of personal support and dependable observation. The quality and availability of personal medical and mental health care is also important. Evaluation of the flier’s flying milieu must include not only routine flying conditions, but also worst-case scenarios involving emergencies, multiple operational stressors, and various personal and situational factors. Clearly, all these factors bear on a given case and no set or standard answer is possible. It is simple to say, ‘‘You will never fly again.’’ It is much more difficult to say, ‘‘Here is how we know that it is now safe for you to fly.’’ What criteria allow the aeromedical practitioner to recommend return to flying duty in a particular case? Reevaluation of such waivers should include considerations of the periodicity of routine physical examinations, the nature of the disorder, the flier’s capacity for accurate self-appraisal and honest action, and the availability of everyday observation from family members and fellow fliers. Most certifying authorities have policies to help determine such matters. To be aeromedically waiverable, the following medical conditions must (30): • Pose no risk of sudden incapacitation • Pose minimal potential for subtle performance decrement, particularly with regard to the higher senses • Be resolved or be stable, and be expected to remain so under the stresses of the aviation environment • Have easily detectable initial signs or symptoms if the possibility of progression or recurrence exists and not pose a risk to the individual or the safety of others • Require no exotic tests, regular invasive procedures, or frequent absences to monitor for stability or progression • Be compatible with the performance of sustained flying operations in austere environments The last of these criteria, which apply to military situations, may not apply to other aviation settings. Certifying authorities should judge mental health conditions using these or somewhat less strict criteria appropriate to the type of flying involved.

LIFE STRESS AND FLYING STRESS Once selected, fliers face not only the stressors of aviation, but also those of everyday life. A flying career does not protect a person from acute stress reactions, psychophysiologic

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disorders, or depression. The coping skills that allow a pilot to deal effectively with inflight emergencies are not the same as those required to deal with family or occupational pressures. Aerospace mental health issues exceed the usual clinical concepts of normality. The aeromedical practitioner must be prepared to recognize and manage mental health disturbances at the preclinical level where they may detract from flying performance, but may not yet have reached the magnitude of clinically diagnosable disorders. Not all mentally healthy (‘‘normal’’) people can fly safely or effectively. Likewise, not all persons with past or present mental health problems are necessarily unsafe or ineffective fliers, hence the existence of waivers. These paradoxic statements arise in part because some people react quite differently to aviation stressors than they do to life stressors. Because aircrew errors are a major source of aircraft accidents, mental health concerns in aeromedical practice must include safety concerns, especially because any ‘‘pilot error’’ involves mental (psychological) factors in some way. Aeromedical practitioners should remain alert for clinical disorders of mental health, and additionally for subclinical symptoms that may affect flying safety or effectiveness. These include symptoms of overstress, anxiety, or depression. Examples include the following: • Increased mistakes in the cockpit or in everyday activities • Distraction by worries or nonproductive, persistent obsession about some problem, especially while flying • Loss of usual sense of humor (one of the best coping skills) • Uncharacteristically reckless behavior • Emotional distress and easy tearfulness • Mood changes, particularly increased irritability or inappropriate anger • Repeated arguments without closure • Hopeless feelings; feelings of being trapped by a problem • Inability to feel happy (anhedonia) • Disturbed sleep, possibly linked to repetitive thoughts • Recent onset of barely disguised or overt FoF • Unexplained weight change • Diminished interest in sex (libido) • Inappropriate concern about somatic symptoms; preoccupation with otherwise minor physical complaints • Increased use of alcohol or sleeping medications Military flight surgeons who have easy medical access to their fliers may be able to take some measures that are more difficult for civilian examiners. Such measures include the following: • Educating fliers about life and aviation stressors; discuss some of the ways that stress-related symptoms appear and what to do about them; continue with discussion of manifestations of life stressors in the aviation arena • Learning to identify the stressed aviator; teaching supervisors and peers to be alert to such signs and symptoms • Making appropriate therapeutic recommendations when needed • Grounding the aviator when necessary, until stressors are past or until the aviator learns better ways of coping

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FEAR OF FLYING Fear of flying is an aeromedical term for a symptom that may arise from many life circumstances. The psychiatric literature does not use this term, although the aeromedical literature has long discussed FoF as if it were a distinct entity. It may be a manifestation of several mental health disorders (31). The only mention of FoF in DSM-IV (7, pp. 405 ff) refers to overt and long-standing ‘‘specific phobias’’ that occur in a small proportion of aircraft passengers; this almost by definition occurs in people who are not aviators. FoF in fliers signals a serial change in their motivation and adaptation. When experienced aviators who previously enjoyed flying become afraid to fly, it may represent a complex mix of acute or chronic causes and symptom presentations. In such fearful fliers, anxiety about symbolic threats may overlay a rational fear of actual risks; this may represent a reaction to a near or actual accident, or displaced anxiety from a personal crisis, or a loss of motivation to fly that threatens the flier’s self-esteem as a competent and powerful person. Whatever its genesis and presentation, symptomatic FoF should medically disqualify any aviator from active flying until the causes are delineated and the underlying disorder has been successfully treated. Such treatment may involve meticulous psychiatric history taking and some psychodynamic exploration, as well as brief pharmacotherapy and behavioral modification techniques (8,31,32).

Postmishap Disorders First, and most obviously, a flier may develop an acute adjustment or PTSD (7, pp. 424 ff) after a flight-related event or mishap. The acute fear may at first be denied or suppressed, but finally overcomes the flier’s defenses and becomes clinically evident. The flier or the physician may easily relate the onset of symptoms to the mishap. The symptom complex may meet the formal diagnostic criteria for an acute adjustment disorder and may progress to PTSD. Because treatment of PTSD is lengthy and difficult, the flier should receive preventive measures and early intervention after any significant mishap. These include a routine discussion of his or her emotional reaction to the mishap, acceptance of the usual initial denial of any negative feelings, reassurance that some bad feelings are normal, and a brief explanation of phenomena such as nightmares, flashbacks, aversions, anxiety, and emotional numbing. The flier’s original and current motivation to fly should be discussed, and the entire matter left open for future discussion. This approach has long been a feature of the aeromedical literature and its principles closely resemble the more formal crisis intervention techniques now used in civil and military disaster situations (33). Current psychiatric research indicates a neurochemical basis for PTSD, and aeromedical practitioners should be alert for possible future recommendations for use of a prophylactic medication within a few hours of an acute traumatic event.

Phobic Disorders Phobic FoF may occur without an obvious antecedent event in a previously unafraid aviator. It may begin insidiously and then worsen in an aviator who has previously enjoyed flying. The flier may be mystified by unpleasant anxieties that may start as exaggerated fear of a specific aviation setting already known to be challenging (e.g., bad weather, night flying) and then extend into other facets of flying. These symptoms are distasteful to the flier (egodystonic) and are usually because of some problem outside of flying, such as burdensome domestic, financial, or life decisions. Because the feared flying situation actually represents displacement onto aviation of anxiety about the underlying life dilemma, the symptoms are disproportionate to the actual aviation setting and the flier may become obsessed by them; for example, checking and rechecking weather reports or attempting to avoid flying at night. Therefore, careful history concerning life situations just before the onset of symptoms is crucial to diagnostic formulation and to treatment. Treatment of flight phobia may consist of a combination of behavioral modification (relaxation and desensitization) with cognitive or insight-oriented talk therapy to identify and deal with the life problem, preferably with an aviationoriented therapist. A few trial flights with another pilot may help demonstrate improved adaptation to flying. Most aviators respond well to this approach because of the egodystonicity of the symptoms and the economic incentive to return to flying, and may resume cockpit duties once their anxiety is allayed. Treatment may include the use of medications only in the initial stage because medications are incompatible with aviation duties.

Somatoform Disorders Somatoform disorders or symptoms represent difficult forms of FoF. These are chronic physical or physiologic symptoms, presented by a professional aviator (sometimes preceded by the words, ‘‘I’d like to fly, but . . .’’) as incompatible with continuing to fly. This presents a striking contrast to the usual attitude of most fliers that they can fly in spite of their symptoms. A reluctant flier’s symptoms arise from an unconscious conflict between anxiety about flying and a greater anxiety about giving up the role of the aviator. ‘‘Involuntary’’ grounding for physical reasons beyond the flier’s conscious control offers an acceptable way out of the conflict. Existing life stressors may accentuate the symptoms. The aviator has no conscious anxiety about flying, and therefore responds to any question concerning apprehension in flight with angry denial because the question represents a challenge to the defense that the symptoms offer against the intolerable but unconscious underlying anxiety. The flier may have little concern about any disease that the symptoms might represent, concentrating instead on being removed from flying duties in order to avoid the distress. The entire presentation case differs from that of the usual aviator who does not want to be grounded. The frustration and irritation of both pilot and physician in dealing with symptoms that are out of proportion to the

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medical situation may indicate the psychological secondary gain involved. Three clinical observations may help identify the unconscious aspect of the symptoms. First, the flier tends to describe the symptoms in terms of their effect on flying. Second, the flier may express no particular anxiety about being significantly ill, and have little interest in specific treatment. Third, if asked, ‘‘Will you go back to flying when you are well?’’ the flier may equivocate or signal reluctance. Identifying the somatoform nature of the problem may allow the physician to avoid unnecessary, expensive, or invasive diagnostic procedures. Even if the psychologic nature of the problem is established, the flier is unlikely to agree with the formulation and to cooperate in necessary psychotherapy. The nature of the symptoms (headaches, various pains, sensory deficits, autonomic disturbances of the gastrointestinal tract) may preclude safe return to flying duties. Once firmly established, somatic presentations of FoF may be quite resistant to therapy (8).

Psychophysiologic Reactions Hyperventilation and syncope, two acute psychophysiologic reactions with aeromedical implications, may occur because of anxiety. Neither is listed in DSM-IV as constituting psychopathology, except for vasovagal fainting responses to injections (7, p. 407), and either reaction may occur in response to physical, situational, or social stressors without the presence of a disease of any kind. Cardiovascular and neurologic disorders must be carefully ruled out, but many episodes of inflight hyperventilation or of ground-based syncope occur in healthy individuals. An episode of spatial disorientation or of hyperventilation in flight may trigger intense symptoms of anxiety. Loss of motivation to fly may undermine previously adequate means of coping with the true dangers of flight, particularly in professional aviators. Interpersonal conflicts with significant individuals in a nonaviation setting (home, office) may precipitate aviationrelated anxiety without any obvious connection to flying except the time of onset. Hyperventilation in fliers may present as an inflight physiologic incident that must be differentiated from hypoxia or exposure to toxic fumes. Once these possible external etiologic elements are eliminated, the physician must rule out any physical reason (cardiac, metabolic, and neurologic) for the symptoms. When spontaneous hyperventilation has been diagnosed, then the physician must establish the reason for the hyperventilation. This usually involves acute or chronic anxiety, or both. Treatment should take into account any underlying situational anxiety such as family pressures, and the more pressing problem of how the flier may deal with the realistic fear that the dangerous symptom may recur. An effective means of addressing incipient hyperventilation is for the flier to control respiratory depth and rate by breathing through the nostrils, which act as flow-limiting valves. Counting the number of seconds of each inhalation and exhaling for twice that count will control the rate. If the inhalation takes 2 seconds, the exhalation should

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last 4 seconds (a 6-second cycle, or a respiratory rate of 10 breaths per minute). Brief practice will demonstrate that hyperventilation is impossible when this technique is followed, and the flier will be reassured that he or she has an effective counter to any future episodes. This reassurance, plus an inflight demonstration if possible, reestablishes the flier’s sense of self-control in the cockpit. Psychogenic syncope may result from loss of sense of control (e.g., spatial disorientation), threats to bodily integrity (e.g., venipuncture, or restraining a child being sutured), and upsetting social situations. The threat may even be implied, as when a flier witnesses a graphic first aid movie. The author has consulted with healthy aviators who have fainted in settings of acute embarrassed anger (male fliers being berated in public by a superior officer where no response was allowed, female fliers responding to subtle unwanted sexual advances) and cultural pressure (continuing to stand at attention at a military ceremony after a long day’s flight, no food and several drinks, despite clear premonitory symptoms of postural hypotension). Such events have the common element of the aviator having to remain passive in the face of a perceived threat, and therefore almost never occur in the cockpit where active response is the norm. Prevention involves teaching fliers to recognize and heed the early warning symptoms of lightheadedness, altered awareness of surroundings, constricted or dim vision, weakness, tingling, and any additional symptoms of orthostasis. Should they recognize the prodrome, the necessary action should be to assume whatever position places the head at or below the level of the heart. This might involve lying down in somewhat unusual situations, but remembering, ‘‘Lie down; pride goeth before a fall!’’ may suffice.

SPECIAL TOPICS Psychoactive Medications Changes in psychoactive medications are coming so rapidly that a textbook discussion of their aeromedical implications should be general rather than specific to avoid becoming outdated. All aeromedical practitioners should maintain at least a general familiarity with current antidepressant and antianxiety medications. Such medications must be used properly, with a clear eye to target symptoms, therapeutic goals, adequate doses, side effects, drug interactions, and previously agreed-upon indications for completion and discontinuation of treatment. Primary care physicians may not be as careful about these factors with patients who have less serious ‘‘adjustment reactions’’ or ‘‘life problems’’ as they are with patients who have major depressive or anxiety-related disorders. Some physicians may even prescribe such medications solely for symptomatic relief, without ever establishing a formal diagnosis or therapeutic endpoint of any kind. Considerable aeromedical discussion involves whether a flier might be safely cleared to fly while taking one of the newer

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antidepressants, particularly the serotonin-specific reuptake inhibitors (SSRIs). A panel of aeromedical psychiatrists and practitioners at the May 1994 Annual Scientific Meeting of the Aerospace Medical Association unanimously agreed that this practice would not be aeromedically indicated for safety reasons. This conservative position is logical and easily understood. However, at least three situations illustrate the problems involved in its inflexibility: 1. Canadian authorities have recently certified six meticulously studied pilots to fly ‘‘with or as a copilot’’ while taking a maintenance dose of individually specified antidepressants: three pilots for chronic depression resistant to drug withdrawal and three for prophylaxis against recurrent depression. These pilots have been carefully followed up for an average of 5 years without incident, representing 30 man-years of experience (M. Lange, unpublished data presented at the U.S. Civil Aviation Medical Association meeting, October 2000), and this may represent the future pattern of aeromedical use of selected psychoactive medications. No published peer-reviewed scientific literature currently supports aeromedically oriented research to cite as a precedent, but two recent abstracts indicate that such reports may be forthcoming (34,35). 2. Medical advisors to the Air Line Pilots Association reviewed approximately 2,500 telephone calls from pilots concerning mental health matters between 1993 and 1997. Of these, 1,200 concerned the prescription of medications for depressive symptoms. Approximately 710 (59%) of the pilots said they had not taken prescribed medications because they would have to stop flying. Another 180 (15%) said they would take the medications and not tell the FAA so that they could continue to fly. Only approximately 300 (25%) said they would take sick leave in order to take the medications, understanding that they would be away from flying for approximately 9 months. Therefore, most commercial pilots either chose to fly with their disorders untreated or to fly while taking medication under aeromedically unsupervised and illicit conditions (D.E. Hudson et al., unpublished data presented at the U.S. Civil Aviation Medical Association meeting, October 2000). Other pilots may well be making the same choices. 3. Physicians may prescribe bupropion HCl or similar medications for control of withdrawal symptoms in smoking cessation programs; the FAA has not approved aviators to use these medications for this purpose. The psychophysiologic effects of nicotine withdrawal pose their own risks to aviation (36), risks that should be balanced against those involved in using medications to help suppress unpleasant symptoms of withdrawal. These three illustrations demonstrate the need for reevaluating existing policies and considering possible criteria for granting waivers or special issuances for the use of some antidepressant medications such as SSRIs under controlled conditions. Aeromedical practitioners should follow the aeromedical literature on this dynamic issue

because some modification in policies will undoubtedly occur in the future.

Air Transport and Aeromedical Evacuation of Psychiatric Patients Psychiatric disorders may result in considerable incapacitation, or in disruptive or dangerous behavior. None of these is compatible with routine airline travel. The physician who must decide whether a person with a mental health disorder can fly alone as a passenger must consider not only routine travel conditions but also the chances that a flight may be delayed or even canceled. The patient may be unable to manage transfers between flights in unfamiliar airports, gate changes, lost luggage, cramped and crowded seating, delayed toilet access, and other disruptions. Upset routines, confusing procedures, lack of privacy, and other inconveniences may unduly agitate some psychiatric patients. The evaluating physician should consider such ‘‘worst-case’’ scenarios, and may usefully consult a knowledgeable family member, neighbor, or friend before deciding whether a psychiatric patient can fly alone, with an attendant, or at all (37). If a psychiatric patient is to travel with an attendant companion, the airline may require prior notification. Careful consideration should be given to medications in such a situation. A psychoactive medication should not be prescribed for travel unless the patient has taken it before, has responded well to it, and has had no undue side effects. An airliner is no place for a patient to suffer an allergic or dystonic reaction, an idiosyncratic response, or a drug–drug interaction. The physician should also consider whether the anticholinergic properties of some medications might slow digestive processes, leading to excessive intestinal gas formation that might be aggravated by increased volume at altitude (37). Passengers who are phobic about flying may benefit by premedication with anxiolytic medications. If multiple flights are necessary, one of the airline-sponsored desensitization programs may be of benefit (31). Aeromedical evacuation of psychiatric patients is a common practice in the military, and experience has shown that proper screening of patients can make this a safe and practical means of transportation. Decisions about the use of psychoactive and sedating medications, litter transport, and restraints should be made conservatively, considering safety of flight and of other patients at all times (38). Such considerations may easily be applied to civilian medical transport situations.

Suicide by Aircraft Aviators have access to aircraft as an instrument of selfdestruction, actions that are unusual but not unknown. A case report of such an occurrence in the early 1970s reviewed the literature to that point (25) and others have been reported since that time. Circumstances vary; some mishaps where self-destruction has been alleged or proved have involved depressed persons who wished to leave their

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families large insurance settlements. Others have involved religious delusions or instances of anger. Some persons have stolen aircraft and been unable to fly them, and some have involved subintentional self-destructive tendencies, such as one in which the flier flew dangerously and foolishly, daring death in a ‘‘Russian roulette’’ manner. Alcohol or drugs may be involved in such actions. Because most aircraft suicides involve litigation, it may be difficult to investigate them in civil or general aviation as evenhandedly as in the military, where legal immunity and the absence of liability issues may allow witnesses more latitude. Investigators must distinguish between a death that occurred because of intentional action and one resulting from foolhardiness, inattention, or negligence. Considerations include elusive personal elements: distraction, longing to get home, sensory overload, fatigue, or external sources of stress. Adding external elements such as depression, illness, romantic misadventures, financial strain, or feelings of hopelessness or guilt make matters more difficult. The diagnosis of suicide by aircraft must begin with the recognition that these events do occur, and clinical suspicion should be raised not only by the circumstances of the death, but also by clinically significant recent events in the victim’s life. As is true elsewhere in medicine, nothing replaces a good history once clinical interest is aroused. Shneidman’s concept of ‘‘subintentional suicide’’ is useful in ambiguous mishaps and the reader is referred to his work for further information on this matter (39).

Aggressive Airline Passengers Airline passengers who become verbally or physically assaultive in flight pose a potential hazard to flight safety, as well as to the safety of crewmembers and other passengers. U.S. Federal Air Regulations 91.11, 121.580, and 135.120 state that ‘‘no person may assault, intimidate, or interfere with a crewmember in the performance of that crewmember’s duties aboard an aircraft being operated.’’ Aircrew report 200 to 300 of these incidents each year (http://www.faa.gov/data statistics/passengers cargo/unruly passengers/). In 1999, the United Kingdom Civil Aviation Authority reported that its air carriers estimated the incidence of serious assaults at 1 in 18,000 flights, and the incidence of all assaults (including minor altercations) as 1 in 870 flights. Alcohol contributed to approximately half these incidents, and smoking (including smoking in aircraft toilets) featured in approximately a third (www.aviation.detr.gov.uk/disrupt/990410/index.htm). Cabin crewmembers, and perhaps cockpit crewmembers, occasionally find themselves involved in verbal and sometimes physical confrontations with passengers. Their management of abusive or assaultive passengers may have medical implications, but is not primarily a medical responsibility. Physicians who are passengers on an aircraft where such incidents occur may be asked to help control the offenders, either verbally or with the use of medications. Although the offender may appear simply to be drunk, differential diagnoses will include mental and physical illnesses with mental manifestations, perhaps complicated by

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acute alcohol or drug intoxication. The offending passenger may also be taking one or several legitimately prescribed medications. In his first aphorism concerning the practice of medicine, Hippocrates warned that the occasion could be instantaneous, experiment perilous and decision difficult. Dealing with a large, aggressive, drunken passenger in the limited confines of an airliner meets these criteria. Although this sort of situation has some similarity to confronting intoxicated and potentially dangerous patients in emergency rooms, those settings include a legally recognized medical interaction amid familiar surroundings, supporting staff, medical supplies and equipment, and access to security personnel. An aircraft is a different setting in these and other respects. No clear legal precedents exist concerning authority to act, liability, permission, or lack of informed or implied consent when dealing with a recalcitrant and oppositional individual. The airliner maybe of one nationality, the passenger of a second, and the physician of a third. The aircraft may be flying over one or several countries, or even over international waters. No explicit medical guidance or peer-reviewed medical citations are currently available for reference. From the psychiatric point of view, the best counsel is to be cautious. Any passenger-physician in such a situation should be aware that the captain may be able to establish a telemedicine link with experienced medical personnel on the ground, and the physician should take advantage of whatever consultation should be available through that modality. The physician present may have much experience in similar settings or may have none. The physician is also a passenger at risk, may have had a drink or two, and may be as emotionally upset as everyone else. Cabin crew and fellow passengers may have unrealistic expectations, and may urge actions that are medically and medicolegally inadvisable or unwarranted. This may be especially true in considering whether to sedate the offender with onboard medications. As noted in the section on Aeromedical Evacuation, one should avoid giving a medication in flight, especially parenterally, that is not known to be safe through experience with its use in the individual on the ground. The prospect is one of giving powerfully sedating medications and possibly supervising involuntary physical restraint of an antagonistic stranger in a crowded and isolated environment with strictly limited medical resources and minimally trained ancillary personnel. The medical history (including prescribed medications) is unknown, the person is not one’s own patient, has not consented to medical services from anyone, and may have consumed an unknown amount of alcohol or illicit drugs. The scenario outlined before appears to be not a medical situation, but one involving safety and security. In more familiar hospital settings, confrontations with assaultive patients are managed by isolating them, and trying to establish an ambience of calm conversation and reason to defuse the crisis. The physician should use a calm and low voice, avoid profanity and confrontational statements or

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threats, remain physically relaxed, and perhaps even adopt a ‘‘thoughtful’’ physical stance (one hand on one’s cheek and the other arm crossed in front of one’s body), but avoid staring at the patient. Signs of increasing agitation include raised voice, physical motion and agitation, clenching and unclenching fists, darting eyes, intrusion into personal space, and physical touching or shoving. When physical restraint proves necessary, an overwhelming, trained, and organized force that ideally includes professional attendants, security, or police personnel should confront the patient. They should accomplish restraint with minimal physical force, taking care to avoid injury if possible. Particular care is necessary when using chokeholds or other maneuvers that may impede not only respiration, but also the blood supply to the brain. The physician may be an onlooker or even an advisor, but may choose not to assume professional responsibility for such proceedings in a nonmedical setting. The aircraft captain, not the physician, is the authority. In summary, caution, prudence, knowledge of situational and professional limitations, and avoidance of overstepping professional boundaries should guide physicians who find themselves in confrontations with their fellow passengers.

Genetics Current active research in the genetics of mental disorders may help predict the chances of occurrence or recurrence of some psychiatric disorders. If genetic analysis improves our ability to evaluate individual fliers, waivers or specific exemptions may be granted with greater precision. Because most psychiatric disorders are now diagnosed by their clinical presentations, rather than by objective tests, identifiable biochemical or genetic markers will represent a great improvement in the accuracy of diagnosis and prognosis for fliers with mental health disorders.

MILITARY ISSUES Deployment and Peacekeeping Missions Peacekeeping missions require repeated or extended periods in foreign and sometimes unpleasant environments. Reservists or other ‘‘part-time warriors’’ may be particularly susceptible to deployment stressors, including disruption of usual activities, financial burdens, uncertain deployment length, changing plans, waiting, boredom, jet lag, fatigue, poor mail or telephone service, lack of privacy, physical discomfort, unpleasant climate, lack of equipment or supplies, abstract or unclear goals, possible or actual terrorism, and a sense of personal danger on the ground as well as in the air. The flight surgeon may not have the power to correct all the stressors that may affect flying safety and effectiveness, but may reduce some by attending to basic amenities like sleep, water, food, and comfort. The flight surgeon should watch for evidence of poor morale such as poor performance or military bearing, loss of the fliers’ usual sense of humor, a rising noneffectiveness rate, increase in alcohol consumption, and minor disciplinary infractions. Unit commanders

and flight surgeons should take stress-related misbehavior seriously, and should rapidly investigate such infractions. Judicious use of time off, recreational facilities, educational and sports programs, civic action programs, and the like may help reduce morale problems that could affect flying safety and effectiveness. When the deployment draws to a close, a formal closure such as a banquet, farewell party, or ceremony may reinforce a sense that the mission was accomplished with honor and purpose.

Flight Surgeon Support to Aviators in Combat Air combat operations add battle stressors to those of deployment. The books by Bond (11) and Grinker and Spiegel (40) are classic basic texts on this subject as observed in World War II fliers. Fliers now tend to be older and better educated, and recent combat operations have been brief and limited, generally flown as sustained operations under conditions of air superiority. However, many factors of aeromedical support to combat operations seem to endure from decade to decade. Combat operations attempt to break the enemy’s will to resist; this includes causing stress-related symptoms among enemy troops while the enemy tries to do the same to friendly troops. Whereas the first medical impulse may be to evacuate symptomatic troops, the essence of leadership and good military medical practice is to return these troops to duties, at least for a while. As with noncombat deployments, flight surgeons should assure that basic amenities are well provided. With the modern emphasis on sustained 24-hour operations, sleeping facilities ought to be quiet and somewhat removed from the flight line, soundproofed and climate controlled for undisturbed rest. Meals should be attractive, nourishing, and available at all hours. Fliers need access to showering facilities and to clean laundry. Attention of base authorities to these services is not only important to the physical comfort of the flier, with its resulting increase in efficient flight, but serves as tangible evidence of the unity with which the base supports the flying mission. Judged by personal accounts, aerial combat is exhilarating to some participants, but as wearing in its own way as infantry combat. As with ground troops, identification with a competent and professional unit is important in dealing with any personal feelings of doubt or fear in combat. Individual soldiers may believe that ‘‘I am the only one who is so frightened,’’ a feeling that contributes to combat fatigue. Frank discussion of fearful feelings by the flight surgeon or the squadron commander help allay the perception of fliers who feel that they alone are experiencing the cognitive and autonomic sensations of fear. The clear message must be that it is normal to be aware of such fear and that the unit accepts it as long as the fliers perform their duties. Combat fatigue is based in part on true physical fatigue, as well as on the internal struggle between an individual’s wish to avoid danger and the wish to face it in order to do one’s duty. Therefore, those responsible for scheduling missions should provide time for sleep; 4 hours of uninterrupted sleep per

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24 hours is the irreducible minimum for the first few frantic days of combat operations, and then schedules ought to allow for 6 to 8 hours of sleep as soon as possible. Much research is being conducted on sleep hygiene in combat operations, including the use of sedative and stimulant medications, and operational flight surgeons must maintain familiarity with current literature and policies, rather than trying to learn about them once hostilities begin. Experienced flight surgeons in previous wars generally have concurred with brief 1- or 2-day rest periods for fliers each week or so, with a longer break (off-base rest and recreation) of approximately 9 days every 6 months. Combat tours should be established as soon as possible; these have traditionally been measured either by number of missions or by number of days in action. These and associated subjects have been thoroughly discussed by Jones (41). There is no ethical way to simulate fear in combat exercises, and fliers may be shocked to recognize their fears in their first few combat sorties. Most fliers will adapt fairly quickly, using defenses they have used before. Because aviators have similar personalities, they tend to use similar defenses: humor, anticipation (planning), suppression, denial, rationalization, intellectualization, and repression (42). Fliers present these elements with exaggerated understatement, bravado, and fatalism in discussions with squadron mates. Flight surgeons have two main ways to prevent or delay combat-related stress symptoms: rest and personal influence. Billeting the flight surgeon with the fliers guarantees medical interest in the elements of rest already discussed. Personal influence (transference) between flight surgeon and flier is crucial. The flight surgeon must provide excellent medical care; nothing will compensate for professional shortcomings. The flight surgeon will assume a role within the squadron as an authority figure, reinforcing fliers’ trust in their own skill, training, and equipment. By sustaining the fliers and also working toward the goals of the unit, flight surgeons help fliers to control their fears by buttressing their coping skills and defenses, rather than by relieving them of their duties. Flight surgeons serve as an informal link in the chain of command, an alternate pathway for getting things done. They should fly as combat observers themselves to establish their credibility, make pertinent aeromedical observations, gain experience useful in dealing with combat stress, and inform commanders about matters concerning combat effectiveness and safety. When combat fatigue is a concern, flight surgeons should see the squadron members everyday in the flight line environment and talk to fliers before and after missions. Inquiries include sleeping patterns, social withdrawal, irritability, temper outbursts, tremors, and abuse of caffeine, nicotine, and alcohol. Early symptoms of alcohol abuse in the combat setting may include fliers’ reports of changing sleep patterns so that they drink in order to get to sleep, or when they or other fliers notice that they are less sharp in the cockpit. Flight surgeons should suspect secondary gain from symptoms when fliers ask to be grounded, or when

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grounded fliers seem in no hurry to get back to flying, miss appointments, ask to stay grounded longer, or ask to be assigned to limited duty. Flight surgeons may depend on the wisdom of line officers about what the squadron can do, and of the fliers themselves about when one of them has ‘‘paid his/her dues.’’ This may help the flight surgeon to decide whether to be tough or sympathetic about symptoms of fear. Regardless of the severity of the military situation, a flier who crashes because of stress-related factors contributes nothing. Military flight surgeons who support combat operations share with their civilian colleagues a responsibility to base aeromedical decisions on the keystone of aerospace medicine, flying safety.

REFERENCES 1. Hart C. The prehistory of flight. Berkeley: University of California Press, 1984:117. 2. Bach R. Stranger to the sky. New York: Dell, 1963:75. 3. Anderson HG. The medical and surgical aspects of aviation. London: Oxford University Press, 1919. 4. Armstrong HA. Principles and practice of aviation medicine. Baltimore: Williams & Wilkins, 1943:2, 460ff. 5. Magee JG Jr. High flight. Newsweek 1942;14:27. 6. Santy PA. Choosing the right stuff: the psychological selection of astronauts and cosmonauts. Westport: Praeger, 1994. 7. American Psychiatric Association. Diagnostic and statistical manual of mental disorders, 4th ed. Washington, DC: American Psychiatric Association, 1994. 8. Jones DR. Flying and danger, joy and fear. Aviat Space Environ Med 1986;57:131–136. 9. Leimann Patt HO. The right and wrong stuff in civil aviation. Aviat Space Environ Med 1988;59:955–959. 10. McGlohn SE, King RE, Retzlaff PD, et al. Psychological characteristics of USAF pilots. AL/AO-TR-1996-0097. Brooks AFB: USAF Armstrong Laboratory, 1996. 11. Bond DD. The love and fear of flying. New York: International Universities Press, 1952. 12. Jones DR, Marsh RW. Psychiatric considerations in military aerospace medicine. Aviat Space Environ Med 2001;72:129–135. 13. Beaven CL. A chronological history of aviation medicine. Randolph Field: School of Aviation Medicine, 1939. 14. Fine PM, Hartman BO. Psychiatric strengths and weaknesses of typical air force pilots. SAM Technical Report 68–121. Brooks Air Force Base: USAF School of Aerospace Medicine, 1968:131–168. 15. Reinhardt RF. The outstanding jet pilot. Am J Psychiatry 1970;127:732–735. 16. Christy RL. Personality factors in selection of flight proficiency. Aviat Space Environ Med 1975;46:309–311. 17. Helmreich R, Gregovich S, Wilhelm J, et al. Personality based clusters as predictors of aviator attitudes and performances. In: Jensen R, ed. Proceedings of the fifth symposium on aviation psychology. Columbus: Ohio State University Press, 1989:607–702. 18. Christen BR, Moore JL. A descriptive analysis of ‘‘Not Aeronautically Adaptive’’ dispositions in the US. Navy. Aviat Space Environ Med 1998;69:1071–1075. 19. Merchant PG, Baggett JC. Aerospace Medical Panel. The concept of aeronautical adaptability as developed by the US. Navy. In: ed. The clinical basis for aeromedical decision making. AGARD CP-553-6. Neuilly-sur-Seine: NATO Advisory Group for Aerospace Research and Development, 1994:14.1–14.7. 20. Mills JC, Jones DR. The adaptability rating for military aeronautics: a historic perspective of a continuing problem. Aviat Space Environ Med 1984;55:558–562.

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21. Edgerton JE, Campbell RJ III, eds. American psychiatric glossary, 7th ed. Washington, DC: American Psychiatric Press, 1994. 22. Santy PA, Holland AW, Faulk DM. Psychiatric diagnoses in a group of astronaut candidates. Aviat Space Environ Med 1991;62:969–973. 23. Kanas N, Caldwell B. Summary of research issues in personal, interpersonal and group dynamics. Aviat Space Environ Med 2000;71(Suppl 9):A26–A28. 24. Zimmerman M. Diagnosing DSM-IV psychiatric disorders in primary care settings. East Greenwich: Psych Products Press, 1994. 25. Jones DR. Suicide by aircraft. Aviat Space Environ Med 1977;48:454–459. 26. Federal Aviation Agency. Guide for aviation medical examiners. Appendix A, Mental Standards. 14 Code of Federal Regulations, Class 1, 67.107.a.l; class 2, 67.207.a.l; class 3, 67.307.a.l. Washington, DC: Federal Aviation Agency, 1996:B1-2, Cl-2, D1-2. 27. Jones DR, Patterson JC. Medical or administrative? Personality disorders and maladaptive personality traits in aerospace medical practice. Aviat Med Q 1989;2:83–91.Reprinted in AGARD AG-324. Neuilly-sur-Seine, France: NATO Advisory Group for Aerospace Research and Development, 1991:19.1–19.4. 28. Flynn CF, McGlohn S, Miles RE. Occupational outcome in military aviators after psychiatric hospitalization. Aviat Space Environ Med 1996;67:8–13. 29. Patterson JC, Jones DR, Marsh RW, et al. Aeromedical management of US Air Force aviators who attempt suicide. Aviat Space Environ Med 2001;72:1081–1085. 30. US Air Force. Medical standards and examination. Washington, DC: US Air Force, 1994. Air Force Instruction 48–123. 31. van Gerwen LJ, Diekstra RFW. Fear of flying treatment programs for passengers: an international review. Aviat Space Environ Med 2000;71:430–437. 32. Jones DR. Fear of flying: no longer a symptom without a disease. Aviat Space Environ Med 2000;71:438–440. 33. Mitchell J. When disaster strikes: the critical incident stress debriefing process. J Emerg Med Serv 1983;8:36–39. 34. Lange M, O’Neill HJ. Serotonin reuptake inhibitors and the depressed pilot [Abstract 101]. Aviat Space Environ Med 2000;71:290. 35. Paul M, Gray G, Lange M. The effect of sertraline on psychomotor performance [Abstract 146]. Aviat Space Environ Med 2001;72:260.

36. Sommese T, Patterson JC. Acute effects of cigarette smoking withdrawal: a review of the literature. Aviat Space Environ Med 1995;66:164–167. 37. Air Transport Medicine Committee. Medical guidelines for airline travel. Washington, DC: Aerospace Medical Association, 1997. 38. Jones DR. Aeromedical transportation of psychiatric patients: historical review and present management. Aviat Space Environ Med 1980;51:709–716. 39. Shneidman E. Definition of suicide. New York: Wiley, 1985. 40. Grinker RR, Spiegel JA. Men under stress. Philadelphia: Blakiston, 1945. 41. Jones DR. US Air Force combat psychiatry. In: Jones FD, Sparacino LR, Wilcox VL, ed. et al. War psychiatry. Washington, DC: Office of the Surgeon General at TMM Publications, Borden Institute, Walter Reed Army Medical Center, 1995:177–210. 42. Vaillant GE. Adaptation to life. Boston: Little, Brown and Company, 1977:383–386.

RECOMMENDED READINGS Jones DR. Military psychiatry. In: Sacks MH, Sledge WH, Warren C, eds. Core readings in psychiatry: an annotated guide to the literature, 2nd ed. Washington, DC: American Psychiatric Press, 1995:781–796. Levy NA. Personality disturbances in combat fliers. New York: Josiah Macy, Jr. Foundation, 1945. Levy RA. Psychiatry. In: Rayman RB, Hastings JD, Kruyer WB, et al., eds. Clinical aviation medicine, 3rd ed. New York: Castle Connolly Graduate Medical Publishing, 2000:289–312. McFarland RA. Human factors in air transportation. New York: McGraw-Hill, 1953. Perry CJG, ed. Psychiatry in aviation medicine. Int Psychiatry Clin 1967;4:1–222. Sledge WH. Aerospace psychiatry. In: Kaplan HI, Freedman AM, Sadock BJ, eds. Comprehensive textbook of psychiatry, 3rd ed. Baltimore: Williams & Wilkins, 1980:2902–2914. Stokes A, Kite K. Flight stress: stress, fatigue, and performance in aviation. Brookfield: Ashgate, 1994.

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Endocrine System and Nephrology Paula A. Corrigan and Curtiss B. Cook

Balance, to my mind, is the key word. —Sir Alexander Campbell

The relative severity of a given condition, and its potential impact on safe aviation performance, are considerations determining the medical certification status of an airman. With respect to flight performance, the effect of any endocrine or renal disorder on cognition, judgment, alertness, consciousness, affect, and stamina pinpoint the primary safety concerns. The medical history of a given aviator is first obtained and summarized with attention to the issues described earlier. The current physical status is then assessed along with any potential treatment. If current medical practice results in ‘‘normalization’’ of an individual with an endocrine or renal disorder, and if the aeromedical risk assessment is determined to be favorable, aeromedical certification may be possible. Diseases of the endocrine and renal systems span a wide variety of disorders, including diseases of glucose and lipid metabolism; the thyroid, pituitary, adrenal, and reproductive function; nephrolithiasis; acute and chronic renal failure; and neoplasms of both systems. It is beyond the scope of this chapter to provide a comprehensive review of the diverse pathology encountered in the fields of endocrinology and nephrology. This section, therefore, focuses on five of the most commonly encountered types of disorders that the aerospace medicine physician will likely encounter: diabetes mellitus, functional thyroid disease, nephrolithiasis, hematuria, and proteinuria.

DIABETES MELLITUS Classification and Diagnosis In 1997, new consensus was reached on the classification of diabetes mellitus. The terms juvenile-onset diabetes

or insulin-dependent diabetes were dropped in favor of the term type 1 diabetes. The terms adult-onset diabetes or non–insulin-dependent diabetes were dropped in favor of the term type 2 diabetes. Other specific types were also recognized (e.g., drug induced). The new nosology was intended to be consistent with contemporary understanding of the pathophysiology for different forms of diabetes (1). In addition to the revised classification of diabetes, a modification was made in diagnostic criteria (1). The principle change was the diagnostic cutoff for fasting plasma glucose level, which was lowered from 140 to 126 mg/dL. The diagnosis of diabetes in a nonpregnant adult is made when one of the following criteria are satisfied: (i) fasting glucose level of 126 mg/dL or more, (ii) 2-hour glucose level of 200 mg/dL or more following a standard 75 g oral glucose challenge, or (iii) a random glucose level of 200 mg/dL plus symptoms consistent with diabetes (e.g., polyuria, polydipsia). When using criteria (i) or (ii), confirmatory testing on a separate day to rule out a false-positive result is required before making the final diagnosis of diabetes. The hemoglobin A1c is not favored to establish the diagnosis of diabetes, although criteria have been proposed (2).

Epidemiology Diabetes mellitus is one of the most common endocrine disorders, affecting approximately 6% of the world’s population (3). Type 2 diabetes constitutes most diabetes cases. Diabetes is epidemic in the United States with an estimated prevalence of approximately 7% of the population (4). Projections about future increases in prevalence predict a continued and rapid rise in the number of affected individuals both nationally and globally (3,5). 425

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Aeromedical Concerns Diabetes mellitus is associated with numerous complications, all of which have potential aeromedical implications. Acute complications may develop that include diabetic ketoacidosis, hyperglycemic crisis, and hypoglycemia. Chronic complications are also critical for aeromedical certification. Diabetes is now the leading cause of adult blindness in the United States, and the number one cause of end-stage renal disease and lower extremity amputations (6). Neuropathic complications can involve both the peripheral and autonomic nervous systems, and the involvement of autonomic nervous system can result in orthostatic hypotension, gastroparesis, bladder dysfunction, and impairment of the patient’s ability to detect hypoglycemia (hypoglycemic unawareness). Individuals with diabetes are at high risk for vascular disease in all vascular territories. Cardiovascular disease remains the leading cause of mortality in diabetes; because of autonomic neuropathy, patients with diabetes may have silent myocardial ischemia (7). In addition to the aeromedical considerations that arise from chronic diabetes complications, additional concerns relate to the direct effects of hyper- and hypoglycemia on cognitive function and those that arise due to medical therapy. Studies have demonstrated impaired cognitive function and mood with an acute rise in blood glucose levels (8). There is also data showing that acute hypoglycemia can lead to impaired nonverbal intelligence, and recurrent hypoglycemia has been reported to lead to permanent neuropsychological impairment (9–11), although this latter finding has not always been consistent (12). Repeated episodes of hypoglycemia can lead to autonomic failure and worsen hypoglycemia unawareness (13). In addition to chronic complications and the impact of extreme glucose values on cognitive impairment, the third aeromedical concern related to diabetes is that of pharmacotherapy. Chronic complications of diabetes are related to the severity and duration of hyperglycemia, hypertension, and hyperlipidemia; simultaneous management of these metabolic abnormalities is needed to prevent or delay the onset of the potentially disabling associated conditions of retinopathy, neuropathy, renal disease, and cardiovascular disease (14–18). Care guidelines, including what targets to achieve for hemoglobin A1c , blood pressure, and lipids are well published (19). Current understanding of the pathophysiology of type 2 diabetes must also take into account the progressive loss of pancreatic β-cell function. Consequently, as the duration of diabetes increases, combined and often complex pharmacotherapies are needed to maintain good glycemic control (20). Eventually, insulin therapy may be needed to achieve glucose targets. These complex therapies for hyperglycemia are typically in addition to the other medications needed to control hypertension and hyperlipidemia. Therefore, polypharmacy may be an issue in the aviator, and the potential side effects and interactions from multiple drugs need to be assessed as part of any aeromedical evaluation. At the time of publication, in the United States, the Federal Aviation Administration (FAA) is the only

aeromedical authority that allows medical certification of noncommercial pilots with type 1 diabetes, and only under strictly limited conditions (see Chapter 11). The FAA, as well as all U.S. military medical authorities, allow some type 2 diabetic patients under good control to fly, with each authority setting specific restrictions (21).

THYROID DISEASE Epidemiology and Diagnosis The most common types of thyroid disease (hypothyroidism, hyperthyroidism, goiters, or nodules) may occur with high frequency in the general population. As many as 50% of persons may have microscopic nodules, 15% palpable goiters, and 10% of the general population an abnormal thyroid-stimulating hormone (TSH) level (22). The prevalence of newly diagnosed hypothyroidism in women is approximately 10 times greater than in men. The prevalence of thyrotoxicosis is 0.5% to 2.0% in women, and is also 10-fold greater in women than in men (23). In addition to female gender, the aeromedical examiner should be aware of other risk factors for thyroid disease including older age, history of previous thyroid dysfunction, presence of other autoimmune conditions, use of certain medications (e.g., amiodarone, lithium), and a family history of thyroid disease. The American Thyroid Association recommends biochemical screening for thyroid disease in asymptomatic individuals beginning at age 35 and then every 5 years thereafter (24). The serum TSH is regarded as the most reliable laboratory method of screening for hypothyroidism and hyperthyroidism in ambulatory patients (24). With the advent of improved TSH assays, instances of subclinical hypothyroidism and hyperthyroidism have been recognized (25). It should be noted that the TSH alone does not identify patients with central hypothyroidism resulting from hypothalamic or pituitary disease. Central hypothyroidism should be suspected in cases where free thyroxine (FT4 ) is low in conjunction with a TSH that is inappropriately low or normal. An elevated TSH accompanied by high thyroxine levels should lead the clinician to suspect either generalized resistance to thyroid hormone or a TSH secreting pituitary adenoma.

Hypothyroidism Primary hypothyroidism is defined as signs and symptoms accompanied by an elevated TSH. A case where the TSH is elevated and the FT4 is normal with minimal or no symptoms is classified as subclinical or mild hypothyroidism. Thyroid hormone has an impact on nearly every organ system, and the severity of hypothyroid symptoms depends on patient age, how rapidly the hypothyroid state evolved, and the presence of other comorbidities. Symptoms are generally nonspecific, and can be confused with other coexisting disorders (e.g., depression). The underlying problem is the slowing of many physiologic processes, but from an aeromedical

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standpoint, the effects of untreated hypothyroidism on cardiac, pulmonary, and behavioral function could have the greatest impact on the aviator. Cardiovascular changes due to hypothyroidism can include bradycardia, increased systemic vascular resistance, and decreased cardiac contractility. Low-voltage and nonspecific ST changes may be seen on electrocardiogram. Up to 40% of persons may have diastolic hypertension. Pulmonary function and respiratory function are also altered in hypothyroidism including conditions such as sleep apnea. Hypercapnia due to decreased ventilatory response to carbon dioxide can occur. The behavioral and neuropsychological symptoms from hypothyroidism are nonspecific. Cognitive impairment, memory deficits, and psychomotor slowing may all be present. Patients may complain of depression, sleep disturbances, and fatigue (23). The signs and symptoms of hypothyroidism are typically reversed with adequate replacement of thyroid hormone. Signs and symptoms that do not resolve after achieving a normal TSH are likely due to some other cause and need to be evaluated. Thyroid hormone replacement is best made with one of the synthetic thyroxine preparations. These are well tolerated and do not have adverse effects that would impair the aviator’s performance.

Hyperthyroidism Thyrotoxicosis is defined as signs and symptoms that accompany elevations in free thyroxine and triiodothyronine, and the TSH is below the lower limit of normal. The term hyperthyroidism refers to sustained increases in thyroid hormone biosynthesis and secretion by the thyroid gland (24). Suppressed TSH levels in the face of normal FT4 and relative absence of symptoms is often referred to as subclinical or mild hyperthyroidism. It is now recognized that even this condition can negatively impact health; subclinical hyperthyroidism is particularly relevant to aeromedical disposition as there is a higher risk of atrial fibrillation (25). The two most common causes of hyperthyroidism the aeromedical examiner is likely to encounter are autoimmune and from a toxic nodule. Nearly every organ system can be negatively impacted by prolonged exposure to elevated thyroxine levels. From an aeromedical standpoint, some of the greatest concerns relate to effects on the cardiopulmonary system, neurobehavioral symptoms, and treatment side effects. Cardiopulmonary manifestations of thyrotoxicosis include decreased systemic vascular resistance, increased cardiac output, tachycardia, and sometimes supraventricular dysrhythmias (e.g., atrial fibrillation). Patients will often experience palpitations. Patients frequently describe tachypnea, dyspnea on exertion, and decreased exercise tolerance. There are physiologic increases in oxygen consumption and minute ventilation, and pulmonary mechanics can be affected with decreased lung compliance and respiratory muscle weakness. Neurobehavioral symptoms can be profound and could have potentially severe implications for flying. Anxiety, dysphoria, insomnia, tremulousness, and cognitive dysfunction can

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be present. Frank psychosis may occur in newly diagnosed thyrotoxicosis, and emotional lability can be severe (23). The therapeutic goal when treating thyrotoxicosis is to return the patient to biochemical and clinical euthyroidism. Adjunctive therapy (e.g., β-blockers) to ameliorate symptoms may be needed until thyroid levels begin to normalize. Treatment of thyrotoxicosis depends on the etiology, but for the most common causes of thyrotoxicosis listed above, one of three methods are usually employed—use of thionamide medications (e.g., propythiouracil or methimazole), ablation with radioactive iodine, or surgical thyroidectomy. Thionamides do have rare adverse events such as marrow suppression or hepatotoxicity, but side effects that are more common include arthralgia, altered taste, or fever; some of these effects could be of aeromedical concern.

NEPHROLITHIASIS Epidemiology and Pathophysiology Nephrolithiasis (renal system stones) is a common urinary tract disorder, affecting approximately 5% of the population, with a lifetime risk of up to 12% of passing a stone. Men are affected more frequently than women, with a ratio of approximately 1.5:1. The peak age for men is 30 years; women have bimodal peaks at age 35 and 55 years (26). Renal stones are frequently an incidental finding in aviators presenting for an examination. Approximately one third of asymptomatic renal stones are expected to become symptomatic within 3 years, with the likelihood related to the location and size of the stone. Once nephrolithiasis is diagnosed, the risk of a recurrent stone is up to 50% within 5 years (27). A family history of stones increases risk by three times; certain medical conditions (insulin resistance, hypertension, primary hyperparathyroidism, gout, surgical menopause) or anatomic abnormalities of the urinary tract are also associated with increased risk. Certain drugs (such as decongestants, diuretics, probenecid, carbonic anhydrase inhibitors, and protease inhibitors) can also predispose to nephrolithiasis. A specific causal factor for renal stones is not found in most cases (26). Low urine volume is the most common associated abnormality, and is the most important factor to address in order to avoid recurrences. Several studies have reported an increased incidence of renal stones compared to the general population in some military aviators, mainly due to dehydration precipitated by austere living conditions or prolonged flights (28,29). Another study demonstrated that increasing daily urinary volume in astronauts just returned from spaceflight reduced the risk of forming renal stones (30). Approximately 70% to 80% of patients with nephrolithiasis have calcium-based stones, most of which are calcium oxalate, or less frequently, calcium phosphate. Hypercalciuria (defined as >200 mg/24 hr or >4 mg/kg/24 hr excreted) is identified in 60% to 80% of calcium stone formers (26). The other main types of stones include uric acid (5%–10%), struvite (15%), and cystine (1%). The same patient may

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be identified with more than one type of stone. Uric acid stones develop when the urine is saturated with uric acid such as occurs with dehydration, or with an acidic pH of the urine. Struvite stones form in patients with urinary tract infections due to urease producing organisms such as Proteus or Klebsiella. Struvite (magnesium ammonium phosphate) is also the most common component of staghorn calculi, which can cause obstruction. Cystine stones are the result of a rare inherited renal defect causing overexcretion of cystine. Stones in these patients usually begin in childhood and can eventually lead to end-stage renal disease.

Patient Evaluation and Treatment The clinical course of a symptomatic aviator with a renal stone is usually that of gradual onset of flank, abdominal, or back pain that progresses to acute colicky pain. Renal colic is usually described as sharp, severe, and localized to the flank, and may be associated with nausea and vomiting. The pain may occur episodically and may radiate anteriorly over the abdomen, or may be referred to the ipsilateral groin area. Once a stone enters the ureter, particularly at the ureterovesicular junction, lower urinary tract symptoms may occur such as dysuria, urgency, and frequency. Urinalysis should be obtained for all patients. Although microscopic hematuria combined with typical symptoms is highly predictive of nephrolithiasis, stones may occur with the absence of blood in the urine (31). Crystals may be present on urine microscopic examination, such as the hexagonal crystals seen in cystinuria, or the ‘‘coffin lid’’ shaped struvite crystals. Urine pH is a valuable clue to the cause of the possible stone; persistent pH below 5.5 is suggestive of uric acid or cystine stones, both usually radiolucent on x-ray films. Persistent urine pH above 7.2 is suggestive of struvite stones. For initial evaluation, a plain kidney-ureter-bladder (KUB) radiograph can be obtained to determine if the stones are radiopaque or radiolucent. Noncontrast helical computed tomography (CT) is the best imaging method to confirm the diagnosis of a urinary stone (99% diagnostic accuracy) in a patient with acute flank pain; it also helps with the measurement of stone density and can detect urinary tract obstruction. Additionally, if the symptoms are not caused by a renal stone, CT can often reveal the true source of the pain. Intravenous pyelogram (IVP) was the gold standard for diagnosis before CT, and is still utilized if CT is not possible. Ultrasonography is rarely used because of its low sensitivity, but is sometimes performed as the initial study in pregnant patients, and is very sensitive for the diagnosis of renal outflow obstruction. An aviator who develops a symptomatic ureteral stone should be grounded until the stone passes or it is removed, because it is possible for incapacitating pain to occur at any time. Most ureteral calculi less than 5 mm in diameter will pass spontaneously within 4 weeks. A recent study found that the α-adrenergic blocker tamsulosin combined with corticosteroids hastened the passage of stones and reduced the need for analgesics (32). Once the acute stone

episode is over, a full metabolic evaluation for possible underlying causes of stone disease should be performed, and any available stones should be analyzed. If a metabolic abnormality is discovered, consideration of prophylactic agents such as thiazides, potassium citrate, or allopurinol may be considered. An increased fluid intake of at least 2.5 to 3.0 L/d is advisable. Dietary modifications may be recommended based on the type of stone, including reduced oxalate intake (such as found in rhubarb, spinach, beets, okra, sweet potatoes, sesame seeds, nuts, chocolate, and soy products), reduced animal protein, and reduced sodium intake. Dietary restriction of calcium is not recommended because calcium consumed at meals (such as in dairy products) may help to reduce oxalate absorption and thereby reduce risk of stone formation (33). Surgical intervention may become necessary if the stone does not pass, refractory symptoms occur, or acute obstruction develops. Extracorporeal shock wave lithotripsy (ESWL) is commonly used to fragment stones in the renal system. ESWL usually has minor complications, and most individuals recover within a few weeks, although recent studies have implicated an increased risk of development of hypertension and diabetes in the long term (34). With the event of the flexible scope, ureteroscopy may now be used to extract stones from the entire urinary tract, and may be used for proximal stones if ESWL fails or is contraindicated. Percutaneous nephrolithotomy (PN) creates an access tract into the renal collecting system through which nephroscopy can be performed, and is typically used for proximal stones, especially for multiple, large (>2 cm), or staghorn calculi. Recovery from PN may take several weeks. There is currently a limited role for open surgery, which has a much longer recovery time and more potential complications.

Aeromedical Concerns Sudden incapacitation in-flight due to the pain of renal colic is the main aeromedical concern associated with renal stones. One study reviewing causes of in-flight incapacitation in United States Air Force (USAF) aircrew revealed three cases of in-flight events over a 10-year period caused by renal colic. All three episodes involved pilots, and in each case, including one single-seat aircraft, the plane landed without incident (35). Another study found renal colic as the cause of nonfatal in-flight incapacitation in 4 out of 42 pilots of International Air Transport Association (IATA) member airlines between 1960 and 1966 (36). Yet another study by the Civil Aerospace Medical Institute (CAMI) revealed that 3 of 39 incapacitating events of U.S. airline pilots during the period 1993 to 1998 were due to renal colic; none were associated with aircraft accidents (37). The issue of asymptomatic retained renal stones or nephrocalcinosis is a difficult one for the aeromedical examiner. As mentioned earlier, there is a 30% chance that an asymptomatic retained stone will become symptomatic within 3 years. Stones retained in the renal parenchyma, or within cysts or calyceal diverticula, are unlikely to migrate into the collecting system and can therefore usually be

CHAPTER 18

followed with serial radiographs or ultrasonography. Stones retained in a papillary duct or more distal kidney parenchyma are more likely to migrate into the collecting system, and may be considered for surgical intervention. Additionally, it is possible that the aviation environment can contribute to the growth and movement of retained renal stones due to voluntary dehydration, extreme temperature, and sedentary work commonly experienced by aircrew. Therefore, it is imperative for aircrew with known nephrolithiasis to remain well hydrated, particularly in the flying environment. Aviators with a single episode of nephrolithiasis are likely to be returned to flying after they are proved to be stone-free with negative metabolic evaluation, by both civil and military aviation authorities. Recurrent or retained stones will require a waiver or special issuance that will depend on the location and type of stone, need for therapy, and complications such as impaired renal function.

HEMATURIA It is common practice to obtain a urine dipstick as part of a flight physical examination for aviators. Therefore, the aeromedical examiner will frequently be required to evaluate microscopic hematuria and proteinuria, both of which can be benign conditions, but can also herald underlying urinary tract or kidney disease. This section addresses the evaluation of hematuria, whereas the next section discusses proteinuria.

Etiology and Diagnosis Hematuria is a fairly common condition. In younger patients, hematuria is transient and benign, and may be secondary to strenuous exercise (such as in a high G-force environment). However, in older patients (>40 years), there is an appreciable risk of malignancy, even if the hematuria is transient, especially in patients with a history of smoking. Hematuria may be visible or microscopic. Gross hematuria is suspected when the urine appears red or brown. As little as 1 mL of blood per liter can induce a visible color change; red or brown urine can also be seen in conditions other than bleeding such as hemolytic anemia, porphyria or the ingestion of beets, blackberries, or certain medications. Gross hematuria is characteristic of lower urinary tract disease and/or bleeding diatheses, and rarely indicates kidney disease, with the exception of cyst rupture in polycystic kidney disease and immunoglobin (IgA) nephropathy. Microscopic hematuria is not visible, but red blood cells (RBCs) are seen on microscopic examination. Definitions vary, but the American Urologic Association requires greater than or equal to 3 RBCs per high-power field to diagnose microscopic hematuria. Dipstick testing for heme may be too sensitive; therefore, a positive dipstick should always be confirmed with microscopic examination. The prevalence of microscopic hematuria is high, occurring in 1.2% to 5.2% in young adult males, and up to 16% of the general population (38). A study of male soldiers with an annual urinalysis performed over a

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12-year period showed a cumulative incidence of transient microscopic hematuria of 39% (39). If microscopic hematuria is persistent on repeat examination, and there is no evidence of a benign cause such as menstruation, vigorous exercise, sexual activity, viral illness, trauma, or infection, then further evaluation is warranted. Hematuria of glomerular origin is frequently associated with an active urinary sediment such as red blood cell casts, dysmorphic red cells, proteinuria, and possibly an elevated serum creatinine. The most common intrarenal sources of hematuria include IgA nephropathy, hereditary nephritis (Alport syndrome), thin-basement membrane nephropathy, or focal glomerulonephritis of other causes. If an intrarenal cause is suspected, referral should be made to a nephrologist for evaluation of primary renal disease with possible kidney biopsy. In the absence of glomerular findings, or if the patient is older than 40 years, a smoker, or has a history of urologic problems per gross hematuria, a urologic referral should be made. Common causes of extrarenal hematuria include stones, infection, and malignancy.

Aeromedical Concerns While transient hematuria is typically benign, persistent or recurrent hematuria may be a sign of significant underlying urinary tract disease and must be fully evaluated in all aviators. Occasionally, a thorough evaluation of the urinary system fails to identify the source of hematuria, thereby posing a dilemma for the aeromedical examiner. Follow-up studies of patients with unexplained microscopic hematuria suggest that these patients have a benign course, and could be allowed to remain on flying status. One study of 191 patients with asymptomatic hematuria that remained unexplained after full urologic evaluation including cytology and cystoscopy showed no cancers detected during longterm follow-up (40). Another study followed 161 Israeli Air Force members with asymptomatic microscopic hematuria over a mean follow-up of 7.6 years. Ninety-one out of 161 of these individuals had no further renal evaluation, but did not develop urologic malignancies or serious progressive renal disorders over the period of follow-up (39).

PROTEINURIA Etiology and Diagnosis Although a wide variety of conditions, ranging from benign to lethal, can cause proteinuria, fewer than 2% of patients whose urine dipstick test is positive for protein have serious underlying urinary tract disorders (41). Urinary protein excretion in the normal adult should be less than 150 mg/d, which correlates with a negative dipstick test. Excretion rates above this define proteinuria and should be evaluated. Alkaline or concentrated urine; gross hematuria; and the presence of mucus, semen, or white blood cells can cause a dipstick urinalysis to be falsely positive for protein. Dilute urine (>1.015) can result in a false negative dipstick. Several factors may lead to mildly increased protein excretion rates

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of up to 300 mg/d (trace to 1+ protein on dipstick) in normal patients. These factors include strenuous exercise (such as during exposure to high G forces), fever, viral illness, or dehydration. If a repeat urine dipstick done at least 48 hours after rest or recovery from illness demonstrates no protein, transient proteinuria is diagnosed, and no further evaluation is indicated. Increased protein excretion (≤1 g/d) upon standing is known as orthostatic proteinuria, a benign condition that occurs in approximately 3% to 5% of adolescents and young adults. If this condition is suspected, overnight urine collection will show less than 50 mg protein excreted for an 8-hour collection (41). For persistent or significant (≥2+) proteinuria, the initial step in diagnosis is careful examination of the urinary sediment for red or white blood cells, casts, or crystals. These findings give useful clues to infection, glomerulonephritis, urolithiasis, or interstitial nephritis, as sources of proteinuria. Concomitantly, a 24-hour urine for protein and creatinine clearance should be initiated to quantify precisely the protein excretion rate. An alternative to the 24-hour urine specimen is the urine protein-to-creatinine ratio (UPr/Cr), determined in a random urine specimen. A UPr/Cr ratio of less than 0.2 mg is equivalent to 200 mg/d of protein excreted and is considered normal (41). Calculation of the glomerular filtration rate (GFR) is also helpful, and can indicate significant renal dysfunction much earlier than changes in serum creatinine will occur. Additionally, one study found that proteinuria in combination with reduced GFR was a significant predictor of cardiovascular disease and all-cause mortality (42). The most common reasons for proteinuria in the range of up to 2 g/d with normal urine sediment and reduced creatinine clearance are diabetes, hypertension, and systemic lupus erythematosus. Therefore, screening should include blood pressure screening, fasting blood sugar, and antinuclear antibodies. Proteinuria greater than 2 g/d suggests glomerular disease, and referral to a nephrologist for further evaluation is indicated.

Aeromedical Concerns Proteinuria is not a disease itself, but suggestive of a possible underlying disorder which could have aeromedical implications. If entities such as hypertension, renal calculi, or diabetes mellitus are found, flying status will be dictated by the underlying problem. It should be stressed that diagnostic steps should be followed logically and expeditiously until a satisfactory explanation of persistent proteinuria is accomplished. Treatment with medications such as angiotensin-converting enzyme inhibitors or angiotensin receptor blockers is recommended for some etiologies of proteinuria, and these are normally well tolerated and compatible with flying duties, if the underlying disease is controlled. Additionally, conditions associated with the aviation environment such as hypoxia or high G forces may cause transient proteinuria with a physiologic basis. There is no evidence to suggest that repeated transient proteinuria related to these factors will cause chronic renal effects in aviators without underlying systemic disease (43).

REFERENCES 1. The Expert Committee on the Diagnosis and Classification of Diabetes Mellitus. Report of the Expert Committee on the Diagnosis and Classification of Diabetes Mellitus. Diabetes Care 1997;20(7):1183–1197. 2. Barr RG, Nathan DM, Meigs JB, et al. Tests of glycemia for the diagnosis of type 2 diabetes mellitus. Ann Intern Med 2003;137: 263–272. 3. Adeghate E, Schattner P, Dunn E. An update on the etiology and epidemiology of diabetes mellitus. Ann N Y Acad Sci 2006; 1084:1–29. 4. Cowie CC, Rust KF, Byrd-Holt DD, et al. Prevalence of diabetes and impaired fasting glucose levels in adults in the U.S. population: national health and nutrition examination survey 1999–2002. Diabetes Care 2006;29(6):1263–1268. 5. Boyle JP, Honeycutt AA, Venkat Narayan KM, et al. Projection of diabetes burden through 2050. Diabetes Care 2001;241:1936– 1940. 6. Centers for Disease Control and Prevention Division of Disease Translation. 1999 Diabetes Surveillance report. CDC’s diabetes public health resource Website. DHHS; 2000. 7. Maser RE, Lenhard MJ. Cardiovascular autonomic neuropathy due to diabetes mellitus: clinical manifestations, consequences, and treatment. J Clin Endocrinol Metab 2005;90(10):5896–5903. 8. Cox D, Kovatchev B, Gonder-Frederick L, et al. Relationships between hyperglycemia and cognitive performance among adults with type 1 & type 2 diabetes. Diabetes Care 2005;28:71–77. 9. Warren R, Allen K, Sommerfield A, et al. Acute hypoglycemia impairs nonverbal intelligence: importance of avoiding ceiling effects in cognitive function testing. Diabetes Care 2004;27:1447– 1448. 10. Wredlin R, Levander S, Adamson U, et al. Permanent neuropsychological impairment after recurrent episodes of severe hypoglycaemia in man. Diabetologia 1990;33:152–157. 11. Langan S, Deary I, Hepburn D, et al. Cumulative cognitive impairment following recurrent severe hypoglycaemia in adult patients with insulin-treated diabetes mellitus. Diabetologia 1991;34(5):337–344. 12. Kramer L, Fasching P, Madl C, et al. Previous episodes of hypoglycemic coma are not associated with permanent cognitive brain dysfunction in IDDM patients on intensive insulin treatment. Diabetes 1998;47(12):1909–1914. 13. Cryer PE. Hypoglycemia: the limiting factor in the glycaemic management of type I and type II diabetes. Diabetologia 2002;45: 937–938. 14. Stratton IM, Adler AI, Neil HAW, et al. Association of glycaemia with macrovascular and microvascular complications of type 2 diabetes (UKPDS 36): prospective observational study. Br Med J 2000;321:405–412. 15. Adler AI, Stratton IM, Neil HAW, et al. Association of systolic blood pressure with macrovascular and microvascular complications of type 2 diabetes (UKPDS 36): prospective observational study. Br Med J 2000;321:412–419. 16. Gaede P, Vedel P, Larsen N, et al. Intensified multifactorial intervention in patients with type 2 diabetes mellitus and microalbuminuria: the Steno type 2 randomized study. Lancet 1999;353: 617–622. 17. Gaede P, Vedel P, Larsen N, et al. Multifactorial intervention and cardiovascular disease in patients with type 2 diabetes. N Engl J Med 2003;348:383–393. 18. Heart Protection Study Collaborative Group. MRC/BHF heart protection study of cholesterol lowering with simvastatin in 20,536 high-risk individuals: a randomized placebo-controlled trial. Lancet 2002;360:7–22. 19. American Diabetes Association. Standards of medical care in diabetes—2007. Diabetes Care 2007;30:S4–S41.

CHAPTER 18 20. Turner RC, Cull CA, Frighi V, et al. Glycemic control with diet, sulfonylurea, metformin, or insulin in patients with type 2 diabetes mellitus: progressive requirement for multiple therapies (UKPDS 49). JAMA 1999;281:2005–2012. 21. Steinkraus LW, Cayce W, Golding A. Diabetes mellitus type 2 in aviators: a preventable disease. Aviat Space Environ Med 2003;74: 1091–1100. 22. Wang C, Crapo L. The epidemiology of thyroid disease and implications for screening. Endocrinol Metab Clin North Am 1997; 26(1):189–218. 23. Braverman LE, Utiger RD, eds. Werner and Ingbar’s the thyroid: a fundamental and clinical text. Philadelphia: Lippincott Williams & Wilkins, 2005. 24. Ladenson PW, Singer PA, Ain KB, et al. American thyroid association guidelines for detection of thyroid dysfunction. Arch Intern Med 2000;160(11):1573–1575. 25. Surks MI, Ortiz E, Daniels GH, et al. Subclinical thyroid disease: scientific review and guidelines for diagnosis and management. JAMA 2004;291(2):228–238. 26. Parmar MS. Kidney stones. Br Med J 2004;328:1420–1424. 27. Pearle MS, Calhoun EA, Curhan GC. Urologic DISEASES in America Project: urolithiasis. J Urol 2005;173(3):848–857. 28. Clark JY. Renal calculi in army aviators. Aviat Space Environ Med 1990;61:744–747. 29. Cramer JS, Forrest K. Renal lithiasis: addressing the risks of austere desert deployments. Aviat Space Environ Med 2006;77:649–653. 30. Whitson PA, Pietrzyk RA, Sams CF. Urine volume and its effects on renal stone risk in astronauts. Aviat Space Environ Med 2001; 72:368–372. 31. Miller NL, Lingeman JE. Management of kidney stones. Br Med J 2007;334:468–472. 32. Dellabella M, Milanese G, Muzzonigro G. Randomized trial of the efficacy of tamsulosin, nifedipine and phloroglucinol in medical expulsive therapy for distal ureteral calculi. J Urol 2005; 174:167–172. 33. Curhan GC, Willett WC, Speizer FE, et al. Comparison of dietary calcium with supplemental calcium and other nutrients as factors affecting the risk for kidney stones in women. Ann Droit Int Med 1997;126(7):497–504. 34. Krambeck AE, Gettman MT, Rohlinger AL, et al. Diabetes mellitus and hypertension associated with shock wave lithotripsy

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36. 37.

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of renal proximal ureteral stones at 19 years of follow up. J Urol 2006;175:1742–1747. McCormick TJ, Lyons TJ. Medical causes of in-flight incapacitation: USAF experience 1978–1987. Aviat Space Environ Med 1991;62: 884–887. Buley LE. Incidence, causes and results of airline pilot incapacitation while on duty. Aerosp Med 1969;40(1):64–70. DeJohn CA, Wolbrink AM, Larcher JG. In-Flight Medical Incapacitation and Impairment of U.S. Airline Pilots:1993 to 1998. DOT/FAA/AM-04/16. Washington, DC: Office of Aerospace Medicine, Oct 2004. Grossfeld GD, Wolf JS, Litwin MS, et al. Evaluation of asymptomatic microscopic hematuria in adults: summary of the AUA best policy recommendations. Am Fam Physician 2001;63(6): 1145–1154. Froom P, Ribak J, Benbassat J. Significance of microhaematuria in young adults. Br Med J 1984;288:20–22. Howard RS, Golin AL. Long-term follow-up of asymptomatic microhematuria. J Urol 1991;145:335–336. Carroll MF, Temte JL. Proteinuria in adults: a diagnostic approach. Am Fam Physician 2000;62:1333–1340. Irie F, Iso H, Sairenchi T, et al. The relationships of proteinuria, serum creatinine, glomerular filtration rate with cardiovascular disease mortality in Japanese general population. Kidney Int 2006; 69:1264–1271. DeLonga DM. Proteinuria in aviation personnel: waiver policy in the U.S. Navy. Aviat Space Environ Med 2003;74:664–668.

RECOMMENDED READINGS American Diabetes Association. Standards of medical care in diabetes—2007. Diabetes Care 2007;30:S4–S41. Braverman LE, Utiger RD, eds. Werner and Ingbar’s the thyroid: a fundamental and clinical text. Philadelphia: Lippincott Williams & Wilkins, 2005. David JR, David PG. In: Ernsting J ed. Aviation Medicine, 4th ed. London: Hodder Arnold, 2006:637–654. Rayman RB, John DH, William BK, et al., eds. Clinical aviation medicine, 4th ed. New York: Castle Connolly Graduate Medical Publishing, 2006:43–47, 277–289.

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19

Infectious Diseases Glenn W. Mitchell and Gregory J. Martin

Diseased Nature oftentimes breaks forth in strange eruptions. —King Henry IV. Part I. Act iii. Sc. 1. William Shakespeare (1564–1616)

HISTORICAL PERSPECTIVE Travel has been a significant vector for infectious diseases since the beginning of time. The spread of the Black Death in the 14th and 15th centuries is a vivid example of the problems of travel when a highly contagious disease is introduced into a nonimmune population (1). People traveled to avoid the plague as it entered their towns, but they were already incubating the disease and only spreading it further. Slow transportation by foot, horse, and carriage kept the plague from exhausting its pool of new victims for many years. The introduction of smallpox, chicken pox, and measles into the New World by Pizzaro and other explorers decimated the indigenous peoples of the Americas and facilitated the cultural dominance of Europeans there. In return, it appears that new world explorers returned to Europe with syphilis, which subsequently became a scourge throughout Europe in the 16th and 17th centuries. Until the late 19th century, lack of understanding of disease transmission led to care for the sick with essentially no effective protective measures for either health care workers or families. However, acceptance of the ‘‘germ theory’’ and recognition of the need for infection control did not eliminate disease spread because transportation advances continued to increase the ability for infections to be transmitted rapidly across great distances. The influenza pandemic of 1918 provides a good illustration of the role of improving travel modes, as coal- and oil-fired ships provided a faster and more convenient way for persons who were ill to continually expose others to novel diseases; the deploying American troops probably brought influenza with them to Europe from their training camps. Cholera is another disease whose history of increasingly rapid worldwide spread is based on improvements in the speed of travel, thereby permitting 432

infectious passengers and crew to arrive in distant ports and establish novel foci of infection. Outbreaks of cholera in South and Central America during the 1980s illuminated the fact that aircraft are also effective vectors for this disease (2). Air travel has become a well-recognized and highly visible risk for transmission of infectious agents. The outbreak of Ebola virus in Kitwit, Uganda, in 1978 demonstrated that persons who are ill might well be flown in commercial aircraft without knowledge of risks by the rest of the passengers. Fortunately, more recent studies have demonstrated that direct contact with body fluids is usually necessary for any significant risk for transmission of this disease. The outbreak and threat of worldwide spread of severe acute respiratory syndrome (SARS) in 2002 to 2003 resulted in quarantines and restrictions on air travel, and focused worldwide attention on the impact of air travel on the rapid spread of potentially serious disease across continents. Most recently, commercial aircraft passengers with active tuberculosis (TB), including one case with an extensively drug resistant (XDR) TB strain, have led to intensive discussions in the press and more indepth investigations of potential problems with spread of infectious diseases inside sealed passenger aircraft cabins (see subsequent text). Recognition of outbreaks of highly pathogenic avian influenza (HPAI) in birds in many areas of the world and associated human cases has appropriately raised concern for rapid transmission of pandemic influenza through air travel. Unlike TB, which generally requires prolonged, close contact, influenza can be relatively quickly and efficiently transmitted. If HPAI becomes adapted to human-to-human transmission, rapid identification and quarantine of infected patients and their contacts will be needed. In 2005, President of the United States, Bush announced at the United Nations the formation of the International Partnership on Avian and

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Pandemic Influenza (IPAPI), which includes management of potentially infected air travelers. The U.S. Department of Health and Human Services has developed a national Pandemic Influenza Plan with specific guidelines for travelassociated influenza in a supplement (3). This chapter will concentrate on diseases of interest to the medical practitioner considering the possible diagnoses for a patient’s illness when the condition is associated with a recent history of air travel.

SIGNIFICANT INFECTIOUS DISEASES Potentially, nearly any infectious agent could be transmitted during air travel. An exhaustive list of potential infectious diseases that could be associated with air travel is too lengthy to compile here. However, a broad sample of significant diseases with their associated common signs and symptoms as well as their relevant characteristics is relevant to the practice of aerospace medicine. For example, travelers may present at varying times after their journey and knowledge of the various incubation periods and geographic locations for common diseases is invaluable. In the interest of brevity, the parasitic diseases and the purely sexually transmitted diseases are not described in this table. These categories of infectious disease do not overlap significantly with those likely to be intentionally spread nor are they commonly spread aboard aircraft. Diseases transmitted in aircraft can be divided as follows: 1. Directly transmitted among passengers. These are mainly respiratory illnesses, and, to a lesser extent, some diarrheal pathogens that can be transmitted in lavatories or through hand-to-hand contact. Viral respiratory pathogens are probably the most commonly transmitted diseases in aircraft. Acute respiratory infections, although exceptionally common, are typically mild. The experience with SARS, and potentially pandemic influenza, demonstrates that very serious respiratory infections may be transmitted in aircraft. These are listed in Table 19-1. 2. Food and waterborne illnesses that are acquired from items served to passengers while on board. These risks are little different from those seen in restaurants and can also be associated with passenger-to-passenger transmission through fomites and are included in Table 19-1. 3. Vector-borne illnesses that are potentially acquired by passengers who are exposed to mosquitoes, sand flies, fleas, or animals that may be intentionally or accidentally on board the aircraft. With the exception of malaria and dengue, transmission of these illnesses aboard aircraft is exceedingly rare; however, the vectors may be transmitted to a nonendemic site and establish the infection in local insects or animals. These potential threats are listed in Table 19-2. 4. Intentionally released agents of bioterrorism such as anthrax, plague, smallpox, and others that could be surreptitiously released in aircraft and with incubation periods would not be detected until the passengers are dispersed throughout the receiving country. Most of the more likely threat agents are listed in Table 19-3.

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Table 19-4 gives their common presenting signs and symptoms. More detailed descriptions of each disease can be found in standard medical references (4,5). Control measures, including isolation and personal protection, as well as currently recommended antibiotics should be used appropriately for each disease. Approximately 50% of travelers to developing countries develop some illness during or after travel and approximately 8% seek medical attention (6). In a country the size of Australia, where 2,000,000 citizens travel overseas each year, this results in approximately 15,000 medical visits. Of course, gastrointestinal infections are most frequent, but various respiratory, cutaneous, and sexually transmitted diseases are also common. The most common life-threatening diagnoses are malaria, dengue, typhoid, amebiasis, and hepatitis. The diagnoses taking the longest time, on average, to manifest are TB, leprosy, and parasitic diseases such as Chagas disease, filariasis, and paragonimiasis. In fact, some do not manifest for months to years after travel. However, more than 90% of these infections (unless the traveler was resident for long periods in developing countries) will become manifest within 6 months of the exposure. Be aware that health problems in immigrants from the developing world often present in the opposite manner, with most infections appearing after 6 months in the new location.

PREVENTIVE ASPECTS OF TRAVEL MEDICINE The best methods of prevention require education of the traveler and include common sense measures such as careful food selection (‘‘cook it, peel it, boil it, or forget it’’), hand washing, avoidance of contact with bodily fluids and lesions, mosquito netting and repellent use, and avoidance of heavily infested areas. Immunization remains the cornerstone of primary prevention of infectious disease. Travelers completing recommended pretravel immunization, such as hepatitis (A and B), yellow fever, rabies, tetanus, polio, measles, mumps, rubella, and varicella, are afforded highly effective protection against these common illnesses. However, other vaccines only reduce—but do not eliminate—the risk of illness, for example, typhoid, meningococcal, and cholera vaccines. Prophylactic medications are the mainstay against several diseases without available vaccines. Diseases with probably effective oral prophylaxis regimens other than vaccines include influenza, plague, leptospirosis, meningococcal meningitis (postexposure), and some types of traveler’s diarrhea. Malaria prophylaxis is complicated by regional variation in the presence of multidrug-resistant strains, and the latest recommendation for a region should be researched on websites of the Centers for Disease Control and Prevention (CDC), and the World Health Organization (WHO), or obtained by consultation with a travel medicine specialist before traveling to malarious areas of the world. Travelers often take medications including antibiotics, purchased either prior to or while traveling, that profoundly

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19-1

Major Vector(s)

Moderate

High: 1–10 organisms

Rarely

Moderately high

Very rarely

Very rarely

High Yes

Aerosol

Fleas (rats); aerosol

Aerosol (birds)

Food; aerosol (infected biologicals)

Contact with infected materials; aerosol

Aerosol (dust and droplets); milk

Melioidosis (Pseudomonas pseudomallei)

Plague (pneumonic Yersinia pestis)

Psittacosis (Chlamydia psittaci)

Q fever (Coxiella burnetti)

Smallpox

Tuberculosis (Mycobacterium tuberculosis)

Moderate

High: 10–100 organisms

High: 100–500 organisms

High: 10–100 organisms

High High

Infectivity

Aerosol droplets; fluids

Person-to-person Spread

Influenza

Respiratory Transmission

Disease

4 wk (usually 1–2) Years

4–12 wk for IPPDa conversion

2–14 d

Weeks to months

1–7 d (usually 2–4 pneumonic)

4–20 d

2–7 d

Illness Duration

7–17 d (usually 12)

10–40 d

4–15 d

2–3 d

2 d–yr

1–3 d

Incubation Period

Infectious Agents Potentially Transmitted Among Passengers in Aircraft

TABLE

Moderate if active disease

High

Low

Very low

Very high (∼100%)

Variable

Low (except for very young and old)

Untreated Lethality

Yes (BCGb is partially effective)

Yes

Yes

No

Yes, but questionably effective for aerosol

No

Yes, but organism mutates easily

Vaccine/Antisera Available?

Yes, but lengthy course of multiple drugs

Experimental antivirals

Yes

Yes

Yes

Yes

Antivirals

Effective Antibiotics?

Worldwide

Nowhere

Worldwide

Worldwide

Worldwide

Southeast Asia, Central and South America, and Caribbean

Worldwide, sometimes in pandemics

Common Geographic Location(s)

435

Body fluids; aerosol

Body fluids; aerosol

Mosquitoes; infected biologicals; aerosol

Ebola virus

Lassa virus

Rift Valley fever

a IPPD, intradermal purified protein derivative. b BCG, Bacille Calmette-Gu´erin.

7–21 d

Moderate

Food, water; fecal/urine

Typhoid fever (Salmonella typhi)

Rarely

Foods/aerosol

Staphylococcal enterotoxin B

6–72 hr (usually 12–36)

1–12 hr

Yes

Food; fecal

Shigellosis (Shigella sp)

High

15–50 d (usually 4 wk)

LD50 = 0.03 µm/person incapacitating

Yes

Food; fecal

Salmonellosis (Salmonella sp)

High

8–12 hr

No

Yes

Food; fecal

Hepatitis A

High

1–5 d

2–5 d

10–14 d

7–9 d

3–12 d

12–96 hr

No

Food, water; aerosol

Clostridium perfringens

LD50 = 0.001 µm/kg for Type A

High

High

High

High

High

No

Food, water; aerosol

Low

Moderate

Moderate

Moderate

Botulism (Clostridium botulinum)

Food and Fomite Transmission

Ticks; body fluids; aerosol

Congo-Crimean hemorrhagic fever

Blood or Body Fluid Transmission

Weeks

Hours to a week

4–7 d

1–3 d

1–2 wk

24 hr

24–72 hr or longer

Days to weeks

1–4 wk

2–21 d

Days to weeks

Moderate (10%)

Low: 2 wk

2–3 wk

Days to weeks

High, if jaundiced (50%), rest are moderate

Usually low; but some strains are 60%

High

Moderate (10%)

High (25%)

Yes Yes

No

No

Yes

Yes

Yes

No

No

Yes

No

Yes

Yes

No

Low/moderate (10%)

Low

Yes

No

Falciparum high; others low

Attacks: days; recurrences: years 1–10 relapses of 2–9 d of fever with 2–4 d between bouts

Yes

No

Low

Yes

Weeks to years

No

High

Can be prolonged

Africa, South and Central America

Central, eastern and Southeast Asia, and South Pacific

Colder areas; especially during war or famine

North America, Asia, and Europe

The United States (April–September)

Africa

Localized, but worldwide

Localized, but worldwide (see CDCa website)

North America, Europe, Asia

South and Central America, Asia, Central Africa, Dominican Republic, Mediterranean basin

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19-3

High High

Moderate No

Ticks; body fluids; aerosol

Body fluids; aerosol

Body fluids; aerosol

Fleas (rats); aerosol

Food; aerosol (infected biologicals)

Contact with infected materials; aerosol

Congo-Crimean

Ebola

Korean (Hantaan)

Plague (pneumonic)

Q fever

Smallpox High: 10–100 organisms

High: 1–10 organisms

Rarely

High

High: 100–500 organisms

High

High

Moderate

Low

Mosquitoes; aerosol

Venezuelan equine encephalitis High: 10–100 organisms

High: 10–100 organisms

No

Deliberate aerosol or in food supply (raw milk)

Brucellosis

Infectivity Moderate: 8,000–50,000 spores

Deliberate or accidental aerosol

Anthrax

Person-to-person Spread No

Major Vector(s)

Disease

7–17 d (usually 12)

10–40 d

2–3 d

4–42 d

7–9 d

3–12 d

2–6 d

5–60 d (usually 1–2 mo)

1–6 d

Incubation Period

Characteristics of Bioterrorist Agents Potentially Released in Aircraft

TABLE

4 wk (usually 1–2)

2–14 d

1–7 d (usually 2–4 pneumonic)

Days to weeks

2–21 d

Days to weeks

Days to weeks

Weeks to years

3–5 d

Illness Duration

Moderate

High

Low

Very high (∼100%)

Yes

Yes

Yes, but questionably effective for aerosol

Experimental

No

Experimental; antisera in Bulgaria

High (∼50%)

Very high (50%–90%)

Yes

No

Aerosol 200 LD50 efficacy in monkeys; antisera experimental

Vaccine/Antisera Available?

Low

Low 2 wk

Years

4–12 wk for IPPDa conversion

Moderate

Hours to a week

1–12 hr

LD50 = 0.03 µm/person incapacitating

24 hr

24–72 hr or longer

8–12 hr

1–5 d

High

LD50 = 0.001 µm/kg for Type A

Yes

No

No

No

High, if jaundiced (50%), rest are moderate

Usually low; but some strains are 60%

High

Moderate (10%)

Moderate (10%)

Moderate if activated

Low: 30 minutes)’’ (10). Aircraft built before the late 1980s usually do not have recirculating air systems, although some have been modified to do so, and all cabin air is taken from outside. Most modern commercial aircraft recirculate 10% to 50% of the cabin air after mixing it with new bleed air in order to provide higher flow rates and lower costs to condition the air for cabin comfort. During cruise flight, an average of 20 air exchanges per hour are accomplished; various aircraft types vary from 5 to 50 air exchanges each hour (11). On the ground and during takeoff and landing, this may be reduced to one third of that value. Recirculating air is also filtered by high-efficiency particulate air (HEPA) filters that remove particles larger than approximately 0.3 µm on modern aircraft, although effective maintenance and protection from moisture are required for most effective filtration performance. Because most bacteria and viruses that are transmitted through the aerosol route are spread through ‘‘droplet nuclei’’ that are typically larger than 5 µm, they are efficiently filtered by HEPA filters. Even so-called weaponized anthrax spores are rarely less than 0.5 µm and therefore would be effectively filtered by a modern, well-maintained aircraft HEPA filter. The effective recirculation and filtration system is easily subverted, however, by individual passenger behavior. No amount of air exchanges and filters can protect against openmouthed coughing and lack of washing of contaminated hands. Simple measures such as using a handkerchief or tissue, and washing hands frequently and before eating, will reduce disease transmission risk significantly. Handling used eating and drinking materials from other passengers in the row during cabin clean up seems an obvious source

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CLINICAL

SCIENTIFIC REPORTS OF DISEASE TRANSMISSION Duct

Airflow

Airflow

Cabin floor Cabin exhaust [Cargo hold]

FIGURE 19-1

Schematic of aircraft cabin airflow.

of contamination if hands are not immediately sanitized afterwards. Hand sanitizing agents are effective when used appropriately, but their liquid/gel composition may restrict them from use in the cabin during periods of high terrorist threat. Current information on prohibited items can be found on the Transportation Security Administration (TSA) website (12). The bottom line is that disease transmission is likely only on flights of more than 8 hours total duration and then only for those sitting within two rows of the infectious passenger. A few highly contagious agents (such as the SARSassociated coronavirus) appear to have been transmitted during flights as brief as 3 hours to passengers several rows away from the index case (9,13). The possibility of more direct contacts among those individuals developing SARS in these situations, however, cannot be totally eliminated. Public health authorities in China and Hong Kong were able to screen patients for fever before boarding aircraft and extensive public education helped minimize additional cases boarding planes. The experience of public health authorities and airlines with SARS actually served as preparation for the looming prospect of pandemic influenza (either an efficiently transmitted mutation of the avian H5N1 strain or a more typical but novel strain). Because influenza is characteristically associated with sudden onset of symptoms, it is possible for someone to board a plane feeling well and become ill during the flight. Influenza can be efficiently transmitted to surrounding passengers but should be filtered by properly functioning HEPA filters. Once pandemic influenza is established, education and screening, along with quarantine measures and follow-up contact information for passengers, will all need to be established. As guidelines are likely to continue to evolve, it will be critical to update practices as per the WHO and CDC websites.

Several infectious diseases have been reported to be transmitted aboard commercial aircraft flights, including SARS, TB, meningitis (detailed in the subsequent text), as well as cholera (14), shigella (15), salmonella (16), influenza (17), and measles (18). Of the reported cases, a majority was food borne illness. Some infections that are potentially transmitted by contact with fellow passengers are discussed in detail in the subsequent text.

Viral Respiratory Diseases Viral respiratory diseases are among the most common infections in humans, and are easily transmitted through respiratory droplet nuclei coughed or sneezed into the environment, and through contact with surfaces where these droplet nuclei land. It is probable that aircraft (or car, bus, or train) passengers surrounding an infected individual, especially if coughing or sneezing, are exposed. Droplet nuclei, typically 5 µm in diameter, are filtered by aircraft HEPA filters. Uninfected individuals, generally within approximately 1 m of an infected individual, may be infected by inhaling droplets suspended in the air. Many respiratory viruses, in the absence of ultraviolet (UV) light, can survive on surfaces for hours to days and can be transmitted by hands to other individuals. Although most viral respiratory infections are relatively mild, two important exceptions must be considered: SARS coronavirus and influenza. The outbreak of SARS in Asia and subsequent spread to Toronto, Canada by air travelers highlighted the role of aircraft in transporting passengers who are incubating an illness, or are mildly ill, to another nation, but also demonstrated transmission of a dangerous viral respiratory infection during flight. Although only four cases of SARS transmission are suspected to have occurred during flight, the significant morbidity and mortality of cases led both the WHO (19) and the U.S. CDC (20) to develop guidelines for aircraft travel if SARS occurs. Current plans for response to a pandemic viral outbreak can be found on the ICAO (21) and International Air Transport Association (IATA) (22) websites. The recommendations currently promulgated for SARS are basic guidance for infectious disease outbreaks and include the following: 1. Screening patients before boarding by checking for fever and asking questions about any symptoms of cough or fever 2. Separating passengers who become ill during flight, as much as possible, from other passengers and giving them a mask to wear to minimize droplet nuclei (if they cannot wear a mask they should be instructed to cough or sneeze into tissues); careful hand washing is critical 3. Requiring staff directly caring for ill passengers to wear masks and use gloves for handling any tissues, secretions, among others from ill passengers; careful hand washing is critical

CHAPTER 19

4. Notifying quarantine stations while the flight is en route so that potentially infected passengers can be isolated and observed on arrival 5. Observing passengers and crew on the aircraft for evidence of disease for 10 days after arrival and instructing them to immediately seek medical attention if they develop symptoms Pandemic influenza is likely to be much more easily transmissible than SARS and will require similar vigilance and measures on board. Travel restrictions from infected areas may be more restrictive than during SARS.

Tuberculosis A flurry of papers reached varied conclusions, but in summary, it appears that person-to-person spread is difficult even in the close confines of tourist class cabins. Investigations have examined possible transmission of Mycobacterium tuberculosis on airplanes involving at least seven different persons with active disease (23–29). One of these investigations documented transmission of M. tuberculosis from a symptomatic index passenger to six passengers with no other risk factors, sitting in the same section of a commercial aircraft during a long flight (>8 hours) (19). However, those documented as exposed did not develop active disease. The remainder of the studies found no significant risk to passengers or aircrew. This is probably due to the fact that M. tuberculosis bacteria, although 0.5 to 1.0 µm in size, are most efficiently spread through droplet nuclei of approximately 5 µm. These particle sizes are completely removed through HEPA filtration of cabin air. Therefore, only direct inhalation of droplet nuclei, before filtration by cabin filters, is associated with significant TB exposure. The WHO recommends the following for medical authorities concerning TB and air transportation: (a) persons with infectious TB should not travel until they become noninfectious (∼2 weeks after beginning an appropriate drug treatment regimen and sputum cultures have become negative), (b) in a patient with suspected or confirmed active TB who has traveled by air during the preceding 3 months, public health authorities should be informed immediately including details of the travel history, and (c) public health authorities should promptly contact the airline company if the patient with known infectious TB has traveled on a flight of at least 8 hours duration during the previous 3 months. Unfortunately, these conservative recommendations, critical to prevent the rare occurrence of aircraft associated transmission of TB, are associated with considerable media attention and often unduly scare passengers despite the fact that it is highly unlikely they have been infected during their flight. Even with rarely documented occurrences of TB infection [i.e., purified protein derivative (PPD) conversion with no active disease] acquired during flights, there has not been documentation of any manifest TB disease in those who were infected (30).

INFECTIOUS DISEASES

443

Meningitis Approximately 12 cases of confirmed meningococcal disease are reported each year to the CDC in which the index patient was on an international flight during the contagious period. The diagnosis is almost never made in transit. As for all contagious diseases, the decision to prescribe antibiotic prophylaxis should be based on (a) the risk of transmission, (b) the difficulty in identifying and notifying passengers affected, and (c) the potential severity of illness. For flights longer than 8 hours, passengers seated directly next to the index patient are more likely to be directly exposed to the patient’s oral secretions and are therefore probably at higher risk than those seated farther from the index patient. In the absence of data regarding elevated risk among other passengers, antimicrobial chemoprophylaxis should be considered for those passengers seated directly next to the index patient. Given the increased frequency of ground delays before takeoff and after landing, one needs to count the total time and not just the air transit time; the more than 8-hour time period should include the total time from when the passengers are seated for takeoff until they disembark. For bacterial meningitis, there are no documented cases of secondary disease among passengers. The CDC, in conjunction with the Council of State and Territorial Epidemiologists, recommends the following actions for meningococcal exposures: (a) household members traveling with the index patient, as well as persons traveling with the index patient who have prolonged close contact (e.g., roommates, members of the same sports team), should be identified, and the need for antimicrobial chemoprophylaxis evaluated; (b) the health department from the state where the patient resides should be contacted promptly to facilitate antimicrobial chemoprophylaxis of household members, day care center contacts, and other possible close contacts; (c) antimicrobial chemoprophylaxis should be considered for passengers who have had direct contact with respiratory secretions from the index patient and passengers seated directly next to the index patient on prolonged flights (>8 hours); (d) CDC and state health departments should enhance surveillance for secondary cases associated with airline travel because identification of such cases would alter these recommendations; and (e) airlines should be responsible for maintaining a passenger manifest to aid in identification of passengers at risk for secondary infections. The CDC should work with airlines to identify the location of potentially exposed passengers. With the assistance of the airline, the CDC should identify the states where these passengers reside and contact the appropriate state and local health officials. The state or local health department will then contact passengers as and when necessary. There is a need for more systematic collection of data on the risk of disease transmission to passenger contacts in order to provide a better basis for public health recommendations (31). At least one recent investigation demonstrated that the only significant effect of air travel bans is likely to be delay of temporal spread of disease, because air travel restrictions after September 11, 2001 in the

444

CLINICAL

United States were associated only with delays in the spread of seasonal influenza viruses (32).

SPACECRAFT ENVIRONMENTS Of course, the spread of disease aboard space vehicles has been recognized as a problem for off-planet travel since the beginning of the space program. Both the spread from one infectious astronaut to fellow crewmembers and the potential for alien organisms to be brought back to earth and its immunologically na¨ıve population have been the subject of elaborate plans and procedures. Last minute changes in crew due to emerging illness or even exposure to infectious diseases in the critical preflight period upset several flights, and the in-flight febrile urinary tract infection of astronaut Fred W. Haise Jr. made the aborted Apollo 13 flight even more memorable than it would have been otherwise. In addition, prime crewmember Thomas K. Mattingly had been exposed to German measles (medical tests revealed that he lacked antibodies and might not be immune), and Jack Swigert replaced Mattingly only days before the launch. On other flights, returning astronauts—and later their moon samples—were isolated immediately upon postflight recovery to reduce the likelihood of bringing an unknown disease back to earth. After the Apollo 11 mission, the astronauts were held in an isolation trailer (Figure 19-2) for 3 weeks, and a surveillance program was conducted among the personnel working with lunar material (33). More recent space experience has demonstrated that biofilms of bacteria also form in space and the microgravity conditions appear to alter some of their characteristics. Escherichia coli form biofilms more readily under simulated spaceflight conditions than do their counterparts grown

FIGURE 19-2 Apollo 11 Mobile Quarantine Facility. The Apollo 11 crewmen, still under a 21-day quarantine, are greeted by their wives as they arrive at Ellington Air Force Base after a flight aboard a U.S. Air Force C141 transport from Hawaii. Looking through the window of the Mobile Quarantine Facility are (left to right) Astronauts Neil Armstrong, Edwin Aldrin Jr, and Michael Collins. The wives are (left to right) Mrs. Pat Collins, Mrs. Jan Armstrong, and Mrs. Jean Aldrin.

under ordinary gravity. Because of the evidence that the Mir space station was heavily colonized by biofilms, this finding could well be applicable to other bacteria. On Mir, severe biofouling damaged quartz windows and corroded various metal surfaces, thereby contributing to a shortened useful lifetime of this station (34). After implementing potential countermeasures to biofilms on the International Space Station (ISS), a study of the ISS environment yielded 12 bacterial strains from the ISS water system. These bacteria consisted of common strains, and colony-forming unit densities were below the usual minimum number required to cause illness. These data indicate that countermeasures based on lessons learned from previous missions have been effective (35).

INTENTIONAL EXPOSURES Currently, the ability of our international travel system to rapidly bring a passenger with an incubating, serious disease into a crowded cabin, a crowded airport, and a na¨ıve population is a serious concern. The potential for an aircraft to transport disease vectors to a new location, where they and their imported disease can also thrive, is an international threat. Moreover, there is concern that someone or some group will use the forced contact of transportation hubs and passenger cabins to purposefully infect unsuspecting thousands and spread a new plague around the world efficiently and effectively. The spread of spores or other fomites aboard aircraft would be difficult due to air handling discussed earlier. Contamination would likely be limited to small volumes surrounding the exposure site, although walking through the aircraft, whereas dispersing an agent would result in large volumes of potential contamination. Contamination of foodstuffs is of limited effect in this era of prepackaged snack foods, although open water containers offer a potential source of pathogen dispersal. Decisions to produce smallpox vaccines again were based, in part, on a fear that the disease could be reintroduced into a population with vanishing immunity to the disease. The toll in death and disability would be enormous. A new smallpox vaccine containing live vaccinia virus is now produced in cell cultures by modern vaccine production techniques (36). Demonstration programs to administer the vaccine to health care workers and others as part of Homeland Security in the United States met with varying degrees of acceptance, but relatively few serious complications have been reported (37). We can only hope that the vaccine will never again have to be used among the general population.

CHALLENGES Innovative techniques, and perhaps improved technology solutions, will be needed to effectively and efficiently screen passengers for infectious disease before boarding commercial aircraft. The SARS outbreak resulted in screening

CHAPTER 19

of passengers by infrared sensors in Asia to ascertain who had fever and therefore needed additional questioning. Additional sensor technology evolution hopefully will yield equipment that is well tolerated by the traveling public in terms of both accuracy and nonintrusiveness. During serious communicable disease outbreaks, or possibly during future high-risk periods involving serious infectious disease threats (e.g., pandemic influenza [38]), some face-to-face screening may also need to be performed at airports. Experience with acceptance of decontamination measures imposed on debarkation from areas where foot-and-mouth disease was prevalent, and the requirement for liquids to be placed in small plastic bags for security checks, indicate that the public can tolerate significant intrusions if there is a perceived threat present. Epidemiologic investigation of cases of serious infections must include detailed travel histories, coordinated with airlines as needed to identify contacts, if a true picture of the implications to others of an index infectious case is to be understood when there has been travel during the relevant communicability period. Travelers need to understand that sitting in an aircraft does not excuse one from the necessities of personal hygiene to reduce the possibilities of disease transmission both to and from fellow passengers. The globalization of commerce has resulted in a rapid increase in travel especially by air. This dramatically increases the opportunities for diseases to be passed to others while symptoms have not yet appeared or while traveling when ill due to job pressures. The high density of travelers aboard aircraft not only presents an opportunity for aggressive organisms but also for the intentional transmission of disease. Serious disease outbreaks facilitated by air travel are likely to occur in the coming years. Practitioners of aerospace medicine must remain aware and knowledgeable of the characteristics of likely diseases if they are to detect outbreaks early enough to effectively interrupt them.

RECOMMENDED READINGS Textbooks Centers for Disease Control (CDC). Health information for international travel, 2005–2006. New Orleans: Claitor’s Law Books and Publishing Division, 2005. Gorbach SL, Bartlett JG, Blacklow NR, eds. Infectious diseases, 3rd ed. Philadelphia: Lippincott Williams & Wilkins, 2004. Guerrant RL, Walker PH, Weller PF, eds. Tropical infectious diseases: principles, pathogens, and practice, 2nd ed. Philadelphia: Churchill Livingstone, 2006. Heymann DL, ed. Control of communicable diseases manual, 18th ed. Washington, DC: American Public Health Association, 2004 (with 2006 update). Mandell GL, Bennett JE, Dolin R, (eds). Mandell, Douglas, and Bennett’s principles and practice of infectious diseases, 5th ed. Philadelphia: Churchill Livingstone, 2000. Nelson KE, Williams CM, eds. Infectious disease epidemiology: theory and practice, 2nd ed. Boston: Jones & Bartlett Publishers, 2007. Pickering LK, ed. 2006 report of the Committee on Infectious Diseases (Red Book Report of the Committee on Infectious Diseases), 27th ed. Elk Grove: American Academy of Pediatrics, 2006.

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Schlossberg D, ed. Current therapy of infectious disease, 2nd ed. St Louis: Mosby, 2001 Strickland GT, ed. Hunter’s tropical medicine, 8th ed. Philadelphia: WB Saunders, 2000.

World Wide Web Sites Centers for Disease Control & Prevention–National Center for Infectious Diseases Travelers’ Health. http://www.cdc.gov/travel/ reference.htm, updated 13 November 2006, accessed 7 July 2007. Centers for Disease Control & Prevention–The Yellow Book - Health Information for International Travel, 2005–2006. An In-depth Travel Reference Book Published Biennially. http://wwwn.cdc.gov/travel/ contentYellowBook.aspx, updated 27 June 2007, accessed 7 July 2007. The Horn of Africa Network for Monitoring Antimalarial Treatment. For extensive malaria links: http://www.hanmat.org/links.htm, updated 18 December 2006, accessed 7 July 2007. Karolinska Institute. For extensive parasitic disease information: http://www.mic.ki.se/Diseases/C03.html. Stockholm, Sweden: Karolinska Institute, updated 26 June 2007, accessed 7 July 2007. Centers for Disease Control & Prevention. For CDC publications and data files: http://www.cdc.gov/publications.htm. Atlanta: CDC, updated 26 April 2007, accessed 7 July 2007. Centers for Disease Control & Prevention. For CDC traveler’s health information on specific areas of the world: http://www.cdc.gov/travel/ destinat.htm, Atlanta: CDC, updated 11 July 2006, accessed 7 July 2007. American Medical Association. For articles and links on emerging infectious diseases: http://www.ama-assn.org/ama/pub/category/ 1797.html. Chicago: American Medical Association, updated 27 June 2005, accessed 7 July 2007. Centers for Disease Control & Prevention–and the Journal of Emerging Infectious Diseases, http://www.cdc.gov/ncidod/eid/index.htm. Atlanta: published by the CDC, updated 29 June 2007, accessed 7 July 2007. Centers for Disease Control & Prevention. Emerging infectious disease resource links from the CDC, http://www.cdc.gov/ncidod/id links.htm, updated 20 June 2006, accessed 7 July 2007. Centers for Disease Control & Prevention. For patient oriented fact sheets and other information on a host of diseases. http://www.cdc.gov/ health/diseases.htm. Atlanta: CDC, updated 19 April 2007, accessed 7 July 2007. For information on various infectious agents communicated by foodstuffs, see The food borne pathogenic microorganisms and natural toxins handbook. http://vm.cfsan.fda.gov/∼mow/intro.html. Washington DC: United States Food and Drug Administration, The Center for Food Safety and Applied Nutrition, updated 25 April 2006, accessed 7 July 2007. World Health Organization. For information on International Travel health requirements and vaccinations as well as travel health advice from the World Health Organization. http://www.who.int/ith/en/, accessed 7 July 2007.

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4. Heymann DL, ed. Control of communicable diseases manual, 18th ed. Washington, DC: American Public Health Association, ISBN 0-87553-034-6, softcover, 2004 (with 2006 update). 5. Gilbert DN, Moellering RC, Eliopoulis GM. The sanford guide to antimicrobial therapy 2006, 36th ed. Hyde Park: Antimicrobial Therapy, Inc, 2006. 6. Looke DFM, Robson JMB. Infections in the Returned Traveller. Med J Aust 2002;177(4):212–219; Also on Internet site: http://www.mja.com.au/public/issues/177 04 190802/ loo10413 fm.html, accessed 7 July 2007. 7. Rayman RB. Aircraft disinsection. Aviat Space Environ Med 2006; 77:733–736. 8. Konheim A. Aircraft disinsection requirements. Internet site: http://ostpxweb.dot.gov/policy/safetyenergyenv/disinsection.htm, accessed 7 July 2007. 9. World Health Organization (WHO). Report of the Informal Consultation on Aircraft Disinsection. WHO: Geneva, Switzerland, Nov 1995. 10. Committee on Air Quality in Passenger Cabins of Commercial Aircraft (National Research Council). The airliner cabin and the health of passengers and crew. Washington, DC: National Academy Press, 2002. 11. Mangili M, Gendreau MA. Transmission of infectious diseases during commercial air travel. Lancet 2005;365:989–996. 12. United States Transportation Security Administration. Permitted and prohibited items: air travel. http://www.tsa.gov/travelers/ airtravel/prohibited/permitted-prohibited-items.shtm. Accessed 7 July 2007. 13. Nagda NL, Fortmann RC, Koontz MD, et al. Airliner cabin environment: contaminant measurements, health risks and mitigation options, Report number DOT-P-15-89-5. Washington, DC: US Department of Transportation, 1989. 14. Eberhart-Phillips J, Besser RE, Tormey MP, et al. An outbreak of cholera from food served on an international aircraft. Epidemiol Infect 1996;116:9–13. 15. Hedberg CW, Levine WC, White KE, et al. An international food borne outbreak of shigellosis associated with a commercial airline. JAMA 1992;268:3208–3212. 16. Tauxe RV, Tormey MP, Mascola L, et al. Salmonellosis outbreak on transatlantic flights; food borne illness on aircraft: 1947–1984. Am J Epidemiol 1987;125:150–157. 17. Moser MR, Bender TR, Margolis HS, et al. An outbreak of influenza aboard a commercial airliner. Am J Epidemiol 1979;110:1–6. 18. Amler RW, Bloch AB, Orenstein WA, et al. Imported measles in the United States. JAMA 1982;248:2219–2233. 19. WHO. Summary of SARS and Air Travel. www.who.int/csr/sars/ travel/airtravel/en/print.html, accessed 7 July 2007. 20. CDC, Guidance about SARS for Airline Flight Crews, Cargo and Cleaning Personnel, and Personnel Interacting with Arriving Passengers, Centers for Disease Control and Prevention, May 2005, http:// www.cdc.gov/ncidod/sars/airpersonnel.htm, accessed 7 July 2007.

21. International Civil Aviation Organization. Aviation medicine section. http://www.icao.int/icao/en/med/medFAQ en.html#health, accessed 7 July 2007. 22. International Air Transport Association. Emergency response plan: public health emergency. http://www.iata.org/NR/rdonlyres/ 1D412DF9-289B-4508-BE9D-A57C4A84F103/0/ AirlinesERPChecklists V1 Nov30.pdf accessed 7 July 2007. 23. Driver CR, Valway SE, Morgan WM, et al. Transmission of M. tuberculosis associated with air travel. JAMA 1994;272:1031–1035. 24. McFarland JW, Hickman C, Osterholm M, et al. Exposure to Mycobacterium tuberculosis during air travel. Lancet 1993;342: 112–113. 25. CDC. Exposure of passengers and flight crew to Mycobacterium tuberculosis on commercial aircraft. MMWR Morb Mortal Wkly Rep 1992–1995;44:137–140. 26. Miller MA, Valway SE, Onorato IM. Tuberculosis risk after exposure on airplanes. Tubercule Lung Dis 1996;77:414–419. 27. Moore M, Fleming KS, Sands L. A passenger with pulmonary/ laryngeal tuberculosis: no evidence of transmission on two short flights. Aviation Space Environ Med 1996;67:1097–1110. 28. Kenyon TA, Valway SE, Ihle WW, et al. Transmission of multi-drug resistant Mycobacterium tuberculosis during a long airplane flight. N Engl J Med 1996;334:933–938. 29. WHO. Tuberculosis and air travel: guidelines for prevention and control. World Health Organization, 1998, http://www.who.int/infpr-1998/en/pr98-96.html accessed 7 July 2007. 30. WHO. International travel and health 2007. World Health Organization, 2007. http://www.who.int/ith/en/, accessed 7 July 2007. 31. Riley LK. Bacterial meningitis exposure during an international flight: lessons for communicable pathogens. Aviat Space Environ Med 2006;77:758–760. 32. Brownstein JS, Wolfe CJ, Mandl KD. Empirical evidence for the effect of airline travel on inter-regional influenza spread in the United States. PLoS Med 2006;3:e401. 33. Brooks GF. Health surveillance of lunar receiving laboratory personnel during the apollo 11 quarantine period. Am J Publ Hlth 1970;60:1956–1959. 34. Matin A, Lynch SV. Investigating the threat of bacteria grown in space. ASM News 2005;70:235–240. 35. NASA. Environmental monitoring of the international space station. http://exploration.nasa.gov/programs/station/EnvironmentalMonitoring.html, updated 6 June 2007, accessed 7 July 2007. 36. CDC. Smallpox vaccination: information for health professionals. http://www.bt.cdc.gov/agent/smallpox/vaccination, accessed 7 July 2007. 37. Schwartz B, Lebwohl M. Complications of the smallpox vaccine. Int J Derm 2005;44:289–292. 38. Evans A, Finkelstein S, Singh J. Pandemic influenza: a note on international planning to reduce the risk from international air transport. Aviat Space Environ Med 2006;77:974–976.

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Dental Considerations in Aerospace Medicine William M. Morlang, II∗

‘‘Dentistry’s Growth in the Last Quarter Century has Reached Aerospace Medicine.’’ Dental practice has changed dramatically over the last 25 years with the current focus being on prevention (1). Additionally, advanced equipment, instrumentation, techniques, and materials have made new options possible when treatment is required. With this growth emerged many subspecialty areas. Aerospace medicine physicians seeking consultation from dental subspecialists, and aviators seeking quality dental care in general, should consider dentists with advanced credentials (Table 20-1).

REACHING AEROSPACE MEDICINE Dentistry plays two major roles in aerospace medicine. First, dentistry contributes to the aviator’s overall wellness. An aviator’s physical standards must include his or her oral and dental health status. Through timely and appropriate oral and maxillofacial examination and diagnostic radiology, dentists are able to assess an aviator while his or her disease is in an early stage. To further promote this wellness, a positive and proactive relationship must exist between the aviator, the dentist, and the aerospace medicine physician. This professional relationship, which includes keen professional communications about the aviator, must be fostered by all more aggressively. The dentist and physician must communicate regarding the dentist’s treatment of and medication prescriptions for their mutual patient. The military health care delivery model provides an example for the civilian community to emulate to ∗ Dr.

Morlang is certified by the American Board of Forensic Odontology. He is a Consultant in Forensic Odontology to the Armed Forces Institute of Pathology. Dr. Morlang is an Adjunct Associate Professor at Tufts University’s School of Dental Medicine. He is a Fellow of the Academies of General Dentistry and Forensic Sciences, the American College of Dentists, and the International College of Dentists. Dr. Morlang served in the United States Air Force for thirty years, attaining the rank of Colonel.

promote such communication, although the Health Insurance Portability and Accountability Act (HIPAA) has several exceptions for the disclosure of protected health information among covered entities to make such communication usually feasible (2). Second, forensic odontology often has the lead role in the identification of deceased aviators and other fatalities after aircraft mishaps, particularly so given the destruction of impact forces and associated fires. Genetic identification of human remains can be done using either nuclear or mitochondrial deoxyribonucleic acid (DNA). Nuclear DNA

TABLE

20-1

Certifying Boards and Professional Organizations Board

Organization

American Board of Endodontics

Academy of General Dentistry American Academy of Forensic Sciences American College of Dentists International College of Dentists —

American Board of Forensic Odontology American Board of General Dentistry American Board of Oral and Maxillofacial Pathology American Board of Oral and Maxillofacial Radiology American Board of Oral and Maxillofacial Surgery American Board of Orthodontics American Board of Pediatric Dentistry American Board of Periodontology American Board of Prosthodontics American Board of Dental Public Health

— — — — — —

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deteriorates rapidly in an aircraft mishap environment, whereas mitochondrial DNA is more stable and therefore used more frequently for forensic identifications. Forensic dental identification of a deceased is a fraction of the cost compared to DNA identification. It is also weeks to months faster. An invaluable asset to forensic odontology has been the military’s repository for duplicate panoral dental radiographs of its military members. Unfortunately, no new dental radiographs are being added currently to this repository. Instead, United States military members’ DNA is being stored in a repository, believed to now have over 5 million specimens. This author maintains that the military’s dental radiograph repository should be continued. On the civilian side, it would be prudent for civilian aviators to place a full-mouth dental radiographic series, a fingerprint card, a footprint card, and a dried blood specimen in their private safety deposit boxes. This could be accomplished with the assistance of civilian dentists, medical laboratories, physicians, and law enforcement agencies. The forensic dental identification process itself is detailed and beyond this chapter’s scope, so it turns now to focus on how dentistry plays a major role in an aviator’s overall wellness.

DENTAL RECORDS Quality record documentation and sound data management are critical to reliable practice management. They are also allies in malpractice prevention and legal defense at all professional levels. Dental records can be in either paper or electronic format. Electronic format is growing in popularity now because of its ease to incorporate digital dental radiographs. An aviator’s dental record must be uniquely marked in the dental practice so that all staff know that they are caring for a patient with special requirements. All health care providers must be acutely aware also of aviators who are in sensitive duty programs. Dental records of these persons must also be uniquely marked for recognition. Treatment notification procedures defined in such sensitive duty programs must be followed, without exception. Quality record documentation enhances proper oral diagnosis, treatment planning, and communication between dentists and aerospace medicine physicians. The United States military services have a straightforward standardization of dental records; however, in civilian practice, a wide diversity of dental forms, charting systems, tooth numbering systems, and abbreviations exists. Attempts, largely driven by the insurance industry, to standardize documentation in civilian dental practice have been only somewhat successful. Nonetheless, an aviator’s dental record should reflect recognized charting methods and symbols, selfintuitive abbreviations, and an accepted tooth numbering system.

Tooth numbering systems are illustrated in most dental anatomy textbooks. The three major systems are Palmer Notation, World Dental Federation Notation of the F´ed´eration Dentaire Internationale (FDI), and Universal Numbering System. The Universal Numbering System assigns each tooth a number, 1 through 32. The sequence begins with tooth number 1—the maxillary right third molar—and continues sequentially around the maxilla to number 16—the maxillary left third molar. The sequence then shifts to the mandibular arch on the left side with tooth number 17—the mandibular left third molar—and continues sequentially around the mandible ending with tooth number 32—the mandibular right third molar. The Universal Numbering System is preferred because it is compatible with the WinID3 forensic identification computer system. WinID3 is presently the premier database program that filters and sorts antemortem and postmortem medical, dental, anthropological, and digital radiographic data to assist in the forensic identification of mass disaster fatalities. In addition to those elements of charting required by state law, a dentist should be sure to chart the following about aviators: privacy compliance, informed consent, all existing dental restorations, missing teeth, prosthodontic/ orthodontic appliances, pathology if noted, treatment plans, treatment delivered, medication prescribed, along with communications with the aviator and aerospace medicine physician. A polished dental practice will also provide the aviator with care instructions delivered both by speaking and in writing. If time is taken to document in a quality fashion, then similar time should be taken to preserve that important data. Simply stated, backup of electronically stored dental record data is paramount. Further, movement of original dental records into combat zones or otherwise ‘‘in harm’s way’’ should first be considered carefully to protect forensic antemortem data that might be required for postmortem identification. Aviators should not transport their own original dental records on the same aircraft that they are flying.

DENTAL RADIOLOGY The field of oral and maxillofacial radiology has excelled dramatically in recent years (3). Modern digital dental radiology systems reduce treatment time, provide almost instant results, afford rapid quality review, and reduce radiation exposure. At a minimum, either a full-mouth series of periapical dental radiographs or a panoral radiograph is essential to have in an aviator’s dental record. The aviator’s record must contain an original radiographic series noted in the preceding text and be augmented with annual bitewing-type radiographs, or as needed, periapical dental radiographs. A new full-mouth radiographic series should be taken every 5 years (or sooner, if significant dental treatment has altered the aviator’s ‘‘dental radiographic profile’’).

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ORAL DIAGNOSIS AND TREATMENT PLANNING Prevention and proper diagnosis are the keys to superior oral health (4,5). The level of oral examination should be commensurate with the aviator’s indicated physical examination. An initial and comprehensive type I examination should include a full-mouth radiographic series, an extensive dental examination, a quality periodontal examination, a complete intraoral soft tissue examination, a palpation of appropriate head and neck lymph node sites, a review of the aviator’s current health history and medications, and a blood pressure screening. Follow-up visits after that may include type II or type III examinations. A type II examination substitutes bitewing-type radiographs for the full-mouth radiographic series. A type III examination requires no new radiographs. Necessity for such follow-up is within the dentist’s discretion, unless otherwise required by agency guideline. At a minimum, the aviator should have at least a type II examination and oral prophylaxis annually. Aviators with histories of significant dental problems should be seen every 6 months. Preventive dental counseling, frequent tooth brushing with fluoride toothpaste, flossing, and fluoridated water consumption are beneficial to maintaining superior oral health (6). Planning for extensive dental treatment for an aviator should be coordinated with his or her aerospace medicine physician before commencement.

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ENDODONTICS AND BARODONTALGIA Dental examination is warranted when an aviator has sensitivity to thermal change, lingering discomfort, swelling of oral soft tissues, oral suppurative discharge, or dental pain (barodontalgia) especially when it is spontaneous or arises when climbing to altitude. Barodontalgia can be debilitating to aviators and may contribute to lack of attention, difficulty in communication, or loss of situational awareness. Sometimes, the specific tooth associated with barodontalgia is difficult to identify. In those cases, percussion of teeth or regional local anesthesia performed by the dentist in an altitude chamber while climbing to 10,000 ft is helpful to diagnosis. Of note, maxillary sinus conditions sometimes project dental pain because of the close association of maxillary bicuspid and molar root tips to the floor of the maxillary sinus. The treatment of dental pulpal disease, a periapical abscess, or barodontalgia usually from severely fractured teeth is generally accomplished by root canal therapy or endodontics (11,12). Instrumented and treated root canals are usually filled with a plastic-type material or silver points and cement. Some forms of endodontic treatment can be done in one sitting. More commonly, root canal therapy is done in multiple sittings. On some occasions, periapical surgery is required to remove localized and walled-off infection in the bone. It is wise for aviators not to fly during the period when the pulp chamber remains unfilled (usually during the first two sittings).

ORAL AND MAXILLOFACIAL SURGERY RESTORATIVE DENTISTRY Generally, dental restorations can be of composite material in anterior teeth and of filled composite material or amalgam in posterior teeth (7). The American Dental Association (ADA) considers dental amalgam (silver filling) to be affordable, durable, and both viable and safe for patients with dental problems (8). Therefore, amalgam may well last longer than most composites and tends to prevent recurrent dental decay. As suggested in the beginning of this chapter, dentistry now offers many new options for treatment (9). For tooth restorations, these include new, stronger composite materials that can be bonded to tooth material especially in posterior teeth and new techniques involving prosthetic facings, which have opened the boutique door for cosmetic veneers (10). Although gaining in popularity among consumers, some cosmetic dentistry techniques often result in a ‘‘cut down’’ of the facial surface of anterior teeth for the placement of prosthetic facings (aesthetic veneers). Such dentists should employ techniques that minimize the risk that an aviator’s veneer might become dislodged in flight with possible resulting pain or aspiration. Great care must also be taken to avoid pulpal involvement.

This specialty, shared by physicians and dentists, affords a wide range of treatment including tooth extraction, surgical removal of impacted teeth, soft tissue and osseous surgery, tumor excision, treatment of head/neck trauma, treatment of facial fractures, and osteotomies for orthodontic or cosmetic reasons (13–15). Few aviators undergo osteotomies because of the lengthy no-fly period after surgery. Aviators should not fly while most multisitting oral surgery procedures are ongoing. They should also not fly for at least 72 hours after the final, postoperative treatment and discontinuation of most medications.

PERIODONTICS This specialty treats diseases of the teeth’s supporting structure. Long-term poor oral hygiene results in plaque formation and dental calculus buildup in the dental sulcus. This results in an increase in depth of the sulcus and periodontal pockets, periodontal abscess, and alveolar bone loss. Normal adult sulcus depth is approximately 4 mm (16). As this depth increases, pockets form where the patient is unable to clean. Infection sets in and tissue and bone are damaged. Periodontists treat early pockets with subgingival

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curettage to clean the area and to create shrinkage. If the pocket depth remains at a level where the patient is unable to maintain the area, periodontal surgery is indicated. In this surgery, the diseased pocket wall is eliminated and the gingival attachment is lowered. Periodontists place periodontal packs to postoperatively protect this surgical area. This pack acts as a template, or form, under which healing occurs. Gingival grafts and bone grafts are not uncommon. Each also requires placement of a periodontal pack. These packs are changed at least weekly until adequate healing has taken place. These packs might interfere with clear speech and could become dislodged. Most periodontal surgery patients are on analgesics and antibiotics, and probably should not fly until cleared by the periodontist and aerospace medicine physician because of the possible risks of pain, bleeding, and periodontal pack dislodgment with potential aspiration thereof. Such occurrences might result in an aviator’s lack of attention, airway obstruction, difficulty in communication, or reduced situational awareness.

PROSTHODONTICS Prosthodontists replace missing teeth with fixed bridges with attached pontics (artificial teeth), implants, removable partial dentures, or full dentures (17–19). Prosthesis dislodgment, aspiration of the prosthesis, and communication problems are major concerns for aviators. Overall, dentists must use great care in constructing, placing, and cementing both individual and temporary crowns to avoid dislodgment and aspiration. Few active aviators wear full dentures. In contrast, bilateral removable partial dentures are more common. Unilateral, removable, partial dentures should be discouraged for aviators because they might be easily dislodged. Fixed crown and bridge prostheses are preferable for them; however, a Maryland Bridge should be avoided because of possible dislodgment. The Maryland Bridge is a three-unit anterior fixed bridge that replaces a missing tooth with a pontic. In this case, the abutment teeth supporting the pontic are prepared with inlay restorations instead of full-coverage crowns. The retentive quality of inlays is less than that of full crowns. Most state laws require identification of dental prosthetic appliances, so dentists should permanently mark the aviator’s name in his or her dentures. This marking will also assist forensic odontologists in the identification process in the event of an aircraft mishap. Of interest, for aviators involved with high-performance fighter aircraft or space flight, some prosthodontists can take extraoral impressions to construct models used in the fabrication of custom oxygen masks, helmet liners, and urine collection devices. Meanwhile, some maxillofacial prosthodontists have superb skills to make facial prostheses for aviators injured in mishaps or disfigured after tumor removal. Artificial eyes, noses, ears, and tissue prostheses—often

secured by magnets—are some prosthodontists’ common creations (20).

ORTHODONTICS Wearing a flight oxygen mask is somewhat uncomfortable while undergoing orthodontic care, but adult orthodontic treatment for aviators is possible. However, orthodontic treatment of an adult takes much longer than treatment of a youth (21). Orthodontists treating aviators must select appliances that have a low risk of dislodgment of their brackets, bands, and arch bars. Aviators undergoing orthodontic care should consider not flying for 24 hours after a major orthodontic appliance placement or major adjustment because of the risk that oral discomfort might be distracting to flight operations.

MEDICATIONS Medications used in general dentistry routinely include antibiotics, analgesics, local anesthetics (with and without vasoconstrictors), nitrous oxide, and intravenous sedation. Dental subspecialists might also use general anesthesia and a much wider variety of systemic medications. For aviators, the impact of these medications on response time, mental processing, coordination, and communication is potentially significant. Dentists should work closely with an aviator’s aerospace medicine physician to evaluate the attending risks and plan flight status accordingly (Table 20-2) (22).

TABLE

20-2

Suggested Duty Not Involving Flying (DNIF) Periods Intervention

Period

Local anesthetic

No flight until 8 hr after administration No flight until 24 hr after root canal is filled No flight until 24 hr after discontinuation No flight until 24 hr after pack is removed No flight until 24 hr after treatment No flight until 72 hr after administration No flight until 72 hr after administration No flight until 72 hr after administration No flight until 10 d after phase I and no flight until 10 d after phase 2

Endodontic treatment Prescription medication Periodontal treatment Orthodontic placement/major adjustment General anesthetics Intravenous sedation Nitrous oxide analgesia Osseointegrated implant

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CARING FOR ASTRONAUTS These aviators should undergo a type I examination upon entry to a space flight program. Thereafter, they should have a type II examination and oral prophylaxis every 6 months. At least 2 months before a mission they should have an additional type I examination. All questionable dental conditions should be evaluated and treated, if indicated. International participants in the National Aeronautics and Space Administration (NASA) program should meet the same dental treatment requirements and physical standards as U.S. participants. Civilian space flight participants should also meet these standards. Astronauts and mission specialists should be trained personally in emergency dental treatment to include oral diagnosis, pain control, local dental anesthesia, dental infection treatment, placement of temporary fillings with Cavit-G, recementing prosthetic appliances or crowns with Dycal, extraction of teeth, and bleeding control. Cavit-G (self-curing zinc oxide composition) and Dycal (calcium hydroxide composition) are materials with characteristics that facilitate their use in a space flight environment. Specific dental instruments, materials, and supplies should be included in a ‘‘dental kit’’ aboard shuttles and space stations (Table 20-3). Analgesics and antibiotics for dental treatment should be determined by the dentist in consultation with the aerospace medicine physician and included in the ‘‘medical kit.’’ Physicians caring for astronauts, mission specialists, or those in long-course residency training should undergo similar emergency dental treatment training and maintain a dental kit. This way they can provide

TABLE

20-3

Sample Dental Kit Analgesics (in medical kit) Anesthesia aspirating dental syringe (2) Anesthesia Carpule 3% Mepivacaine HCl (12) 4% articaine HCl with 1:100,000 epinephrine (12) Anesthesia syringe needle 27gauge long (12) Antibiotics (in medical kit) Cavit -G (one jar, or two tubes) COGSWELL-A elevator (1) Cotton balls (dental, one pack) Cotton pliers (2) Cotton rolls (dental, 1 pack) Dycal (2 tubes and applicator)

Examination gloves (10) Excavator (small, 2) Explorer (2) Extraction elevator no. 301 (1) Extraction forceps no. 150 (1) and no. 151 (1) Front surface dental mouth mirror (2) Gauze/sponge (2 × 2 in) (2 packs) Handheld light (2) with batteries Instrument disinfection packets (25) Periodontal scaler (2) Woodson plastic instruments (2) — —

The numbers indicated in parentheses refer to quantity. HCl, hydrochloride.

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dental care in remote settings if needed in a dentist’s absence.

CONCLUSION With this chapter’s premier in this text’s fourth edition, it follows that aviators, dentists, and aerospace medicine physicians should embrace the opportunity to incorporate oral and dental health into aviators’ physical standards to promote their overall wellness from their training on the ground to their aerospace flight.

REFERENCES 1. Harris NO, Garcia-Godoy F, eds. Primary preventative dentistry, 6th ed. Upper Saddle River: Pearson Prentice Hall, 2004. 2. Health insuranc eportability and accountability act of 1996, 45 C.F.R. §§164.502, 164.506, 164.512 (October 1, 2006). 3. Langland OE, Langlais RP, Preece JW. Principles of dental imaging, 2nd ed. Baltimore: Lippincott Williams & Wilkins, 2002. 4. Burket LW, Greenberg MS, Glick M, eds. Burket’s oral medicine: diagnosis and treatment, 10th ed. Hamilton: BC Decker, 2003. 5. Cawson RA, Binnie WH, Barrett AW, et al. Oral disease: clinical and pathological correlations, 3rd ed. Edinburgh: Mosby, 2001. 6. Wilkins EM. Clinical practice of the dental hygienist, 9th ed. Philadelphia: Lippincott Williams & Wilkins, 2005. 7. Francischone CE, Vasconelos LW, eds. Metal-free esthetic restorations: procera concept, 2nd ed. Sao Paulo: Quintessence, 2003. 8. American Dental Association. Statement on dental amalgam (updated April 6, 2007). Available at: http://www.ada.org/prof/ resources/positions/statements/amalgam.asp (last visited July 14, 2007). 9. Summitt JB, Robbins JW, Hilton TJ, et al. eds. Fundamentals of operative dentistry: a contemporary approach, 3rd ed. Chicago: Quintessence, 2006. 10. O’Brian WJ. Dental materials and their selection, 3rd ed. Chicago: Quintessence, 2002. 11. Okeson JP, Bell WE. Bell’s orofacial pains: the clinical management of orofacial pain, 6th ed. Chicago: Quientessence, 2005. 12. Walton RE, Torabinejad M. Principles and practice of endodontics, 3rd ed. Philadelphia: WB Saunders, 2002. 13. Donoff RB. Massachusetts general hospital manual of oral and maxillofacial surgery, 3rd ed. St. Louis: Mosby, 1997. 14. Fonseca RJ. Oral and maxillofacial surgery, Vol. 7, 1st ed. Philadelphia: WB Saunders, 2000. 15. Fonseca RJ. Oral and maxillofacial trauma, Vol. 2, 3rd ed. Philadelphia: WB Saunders, 2005. 16. Rose LF, Mealey BL, Genco RJ, et al. Periodontics: medicine, surgery and implants. St. Louis: Mosby, 2004. 17. Rosenstiel SF, Land MF, Fujimoto J. Contemporary fixed prosthodontics, 4th ed. St. Louis: Mosby, 2006. 18. Pheonix RD, Cagna DR, DeFreest CF, et al. Stewart’s clinical removable partial prosthodontics, 3rd ed. Chicago: Quintessence, 2003. 19. Zarb GA, Bolender CL, Eckert S, et al. Prosthodontic treatment for endentulous patients: complete dentures and implant-supported prostheses, 12th ed. St. Louis: Mosby, 2004. 20. Beumer J, Curtis TA, Marunick MT, eds. Maxillofacial rehabilitation: prosthodontic and surgical considerations. St. Louis: Medico Dental Media International, 1996. 21. Graber TM, Vanarsdall RL, Vig KWL, eds. Orthodontics: current principles and techniques, 4th ed. St Louis: Mosby, 2005. 22. Air Force Instruction 47–101, Department of the Air Force, May 2000.

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RECOMMENDED READINGS Burket LW, Greenberg MS, Glick M, eds. Burket’s oral medicine: diagnosis and treatment, 10th ed. Hamilton: BC Decker, 2003. Cawson RA, Binnie WH, Barrett AW, et al. Oral disease: clinical and pathological correlations, 3rd ed. Edinburgh: Mosby, 2001. Okeson JP, Bell WE. Bell’s orofacial pains: the clinical management of orofacial pain, 6th ed. Chicago: Quientessence, 2005.

Scully C, Cawson RA. Medical problems in dentistry. Edinburgh: Elsevier Science, Churchill Livingstone, 2005. Short MJ, Levin-Goldstein D. Head, neck and dental anatomy, 3rd ed. Clifton Park: Thompson/Delmar Learning, 2002. Thaller SR, Montgomery WW. Guide to dental problems for physicians and surgeons. Baltimore: Williams & Wilkins, 1988.

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21

Occupational and Environmental Medical Support to the Aviation Industry Roy L. DeHart and Steven M. Hetrick

There are many things that a doctor, on his first visit to a patient, ought to find out either from the patient or from those present. For so runs the oracle of our inspired teacher: ‘‘When you come to a patient’s house, you should ask him what sort of pains he has, what caused them, how many days he has been ill, whether the bowels are working and what sort of food he eats.’’ So says Hippocrates in his work AFFLICTIONS. I may venture to add one more question: what occupation does he follow? —Bernardino Ramazzini 1713 (1)

The men and women of the aerospace industry, both those on the ground and in the air are exposed to hazards of injury and illness beyond that that is unique to the flying environment. Occupational injuries and exposures are all too common in the workplace and aerospace presents numerous hazards. This chapter provides an opportunity for the student or casual reader to become familiar with the policies and procedures in the United States that have been developed to prevent or manage workplace morbidity and mortality. Similar policies and procedures are at work to prevent or reduce the harm to the public that is present because of aviation activities. Such risks include transmission of disease by a large fast-flying vector—the aircraft or spacecraft. Arthropods, infectious carriers, and formite transmission have all been transported by aircraft. To some the aircraft becomes a potential hazard to the environment because of the jet or rocket exhaust. This chapter is presented in two major sections: occupational hazards and environmental concerns.

SECTION ONE: OCCUPATIONAL MEDICINE The American Board of Preventive Medicine defines occupational medicine as that specialty which focuses on the health of workers, including the ability to perform work; the physical, chemical, biological, and social environments of the workplace; and the health outcomes of environmental exposures. Practitioners in this field address the promotion of health in the workplace and the prevention and management of occupational and environmental injury, illness, and disability (2). In 2005 Paul A. Schulte, PhD a researcher at the National Institute for Occupational Safety and Health (NIOSH), Centers for Disease Control and Prevention (CDC), published an article regarding the national burden of occupational injury and disease on the nation. His research demonstrated that the burden of occupational injury and illness is substantial among America’s workforce. In 2002, the Bureau of Labor Statistics (BLS) reported more than

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5,500 fatal work injuries, 4.4 million nonfatal injuries, and 294,500 illnesses. In the same year, NIOSH estimated that 3.6 million occupational injuries and illnesses were treated annually in U.S. hospital emergency rooms. His research further addressed a $72.9 billion expense to employers for worker’s compensation premiums with a total direct and indirect cost estimated to be in the range of $128 to $155 billion (3). Each year there is a survey of occupational injury and illness across the United States. This is a federal/state program in which the employer reports are collected from private industry. The survey measures nonfatal injuries and illness and excludes self-employed. farms with fewer than 11 employees, private households, federal government agencies, and the national data system employees in state and local government agencies. The survey provides estimates of the incident rates of the injuries and illnesses based on logs kept by the industry employers during the year. The most current data available (2005) is summarized by industrial sector beginning with the highest incident rate of illness and injury. These data are summarized in Table 21-1. The overall national incident rate was 4.6 cases per 100 equivalent full time workers during 2005. The census of fatal occupational injuries is also a part of the BLS Occupational Safety and Health statistics program compiled for the United States each calendar year. The data set contains information about each workplace, worker characteristics, equipment being used, and the circumstances of the fatal event. In his preface to the Occupational Medicine State of the Art Review titled The Aviation Industry, Dr. Kendall Green commented that occupational aviation medicine is an amalgam of two specialties of preventive medicine: occupational medicine and aviation medicine (4). He further noted that as a part of preventive medicine, occupational and aviation medicine include the public health and epidemiologic perspectives in addition to the perspectives

TABLE

21-1

Nonfatal Workplace Injury/Illness Rates by Labor Sector in 2005 Industry Sector Transportation Construction Manufacturing Agriculture, forestry Leisure and hospitality Health and social Utilities Wholesale and retail Mining Professional and business Information Financial

Rate per 100 Employees 7.0 6.3 6.3 6.1 6.1 5.7 4.6 4.1 3.6 2.4 2.1 1.7

of ‘‘what’s best for my patient’’ commonly seen in clinical medicine. Aerospace medicine and occupational medicine are part of international coalitions of specialty medical practice. In much of the world, the term occupational medicine is better translated in the broader term of occupational health. The World Health Organization (WHO) in 1950 undertook to define ‘‘occupational health’’ as follows: Occupational health should aim at the promotion and maintenance of the highest degree of physical, mental, and social well-being of workers in all occupations; the prevention among workers of departures from health caused by their working conditions; the protection of workers in their employment from risks resulting from factors adverse to health; the placing and maintenance of the worker in an occupational environment adapted to his physiological and psychological equipment; and to summarize, the adaptation of work to man and of each man to his job.

In more modern times, the gender bias has been removed and it is well recognized that we have people of both genders actively participating in the workplace. It was within the context of this definition that the specialty of occupational medicine became formalized. In 1955, a certification program in occupational medicine was established by the American Board of Preventive Medicine. As of 2007, a total of 3,609 physicians have been certified in occupational medicine as compared to 1,423 in aerospace medicine (5). A key element of both occupational and aerospace medicine is their focus on prevention. Many of the tools used by the profession are those that address illness and injury prevention as well as the clinical topics involved with treatment and management of afflictions, impairment, and disability. Service is provided to a workforce with a demographic characteristic that remains predominantly male in the age-group between 18 and 65. Because of the requirements of employment, most workers are in better health than the general population and enjoy a middle class living standard. In epidemiologic studies that address this population, a term identified as the healthy worker effect is important in studying cohorts that are compared with worker populations. Workers in general are in better health with less morbidity and lower mortality when compared to the general population even when gender and age adjusted because they are an employed cohort. The workplace in the aerospace industry incorporates many of the materials, processes, and operations common to manufacturing in general: airplane repair and maintenance that includes drilling, riveting, screwing, fastening, welding, painting, aluminum layout, template work, subassembly, fuselage fabrication, manipulating large units, replacing of motors, engines, propellers, turbines, wing sections, electronics and avionic equipment, and the inspection of planes, equipment, and machine tool repair. Further, it is often the aviation industry that introduces new machine processes such as the fabrication of titanium structures and

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TABLE

O C C U PAT I O N A L A N D E N V I R O N M E N TA L M E D I C A L S U P P O R T ...

21-2

Work-Related Medical Problems Seen in the Aerospace Workforce Cuts and lacerations Dermatitis Contact Allergic Foreign body in eye Infections Repetitive trauma Carpal tunnel syndrome Tenosynovitis Raynaud’s syndrome Respiratory tract reaction Neurosensory hearing loss Neurotoxic reaction Central Peripheral Strains and sprains Low back Cervical Shoulder

the buildup of metal and carbon fiber composites. Common work-related medical problems occurring in the aerospace industry are enumerated in Table 21-2 (6). Specialists in aerospace medicine must develop and maintain sufficient orientation and knowledge in the fields of occupational and environmental medicine (OEM) to assist management in obtaining and using the consultation necessary to prevent and solve problems that involve potential toxic hazards arising out of planned operations, products, and waste. In this way, aerospace medicine is better able to encompass the total program of preventive medicine in support of this national industry that is so critical to the economy and national defense.

HISTORY The relationships of types of work to illness were first addressed by Hippocrates. Centuries later, Ramazzini in his treatise Disease of Workers described a constellation of afflictions that befall workers in more than 50 occupational settings (1). As the book was published in the 1700s, it would be surprising if it mentioned anything regarding the aviation industry. Early in the last century, Alice Hamilton, a professor at Harvard’s College of Public Health began to visit American industries in the eastern United States documenting her observations and making recommendations to improve the lot of the worker. Her autobiography Exploring the Dangerous Trades details some of her experiences with American industry (7). More recently, Dhenin, a leader in aviation medicine in the United Kingdom observed that aviation medicine is a

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branch of occupational medicine developed from the need to adapt humans to the hostile environment of the air (8). Although within the United States this observation may be considered controversial by some, it does have its advocates. This recognizes the close relationship between aerospace medicine and occupational medicine, particularly when considering commercial airline and military operations. In 2005 among the major airlines in the United States, only 20% of employees were flight deck personnel and flight attendants, whereas the remaining 80% were classified as ground personnel. Although flight personnel are potentially exposed to many of the hazards unique to flight as described in detail in several chapters of this text, they are also susceptible to occupational illnesses and injuries similar to their ground personnel cohorts. The U.S. Department of Labor annually publishes labor statistics that include the aviation industry. Table 21-3 lists the type and number of workers in various categories divided roughly into airline operations and aviation manufacturing and maintenance. These figures provide a glimpse of the complexity of the workforce and its distribution in specialties across the industry (9). To provide a different perspective, the classification of the workforce for a large U.S. international airline hiring approximately 100,000 workers is given in Table 21-4 (10). In recent years, there has been a considerable downsizing of many of the U.S commercial airlines resulting from cost pressure. The head count has become very sensitive to the

TABLE

21-3

Employment in Various Occupational Categories Across the Aviation Industry including Manufacturing, Maintenance, and Airline Operations Airline operations Flight attendants Licensed pilots, co-pilots, and flight engineers Air traffic control Airfield operations Ticket agents Baggage handlers Production workers (other) Helpers not otherwise classified

99,030 26,240 21,590 4,500 97,960 9,540 2,470 2,090

Aircraft manufacturing and maintenance Aerospace engineers Aircraft structural systems Aircraft mechanics and service technicians Operations technicians Sheet metal workers Electricians Aviation technicians Computer specialists Maintenance personnel Cargo

40,860 20,510 18,070 5,280 4,070 1,230 4,720 2,040 40,930 2,350

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TABLE

21-4

TABLE

International Airline Personnel Positions Position Maintenance and ramp personnel Flight attendants Agent/planner Pilots Management Reservation representatives Staff support Total number of employees

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Occupational and Environmental Health Services Number 32,000 20,000 13,200 11,700 8,536 6,500 3,200 95,000

bottom line. For example, in 2003 Delta Air Line’s head count was 70,600 employees with a fleet of 833 planes and a cost of 9.36 cents/mi. In 2006, the employee numbers had dropped to 51,000 with a fleet of 625 planes and a cost per seat mile of 6.91 cents (11).

ESTABLISHING AN OCCUPATIONAL AND ENVIRONMENTAL MEDICAL PROGRAM First and foremost, occupational medicine is a specialty of medicine that is a discipline within preventive medicine. The major goal is to prevent injury and disease and should this not be entirely effective, to prevent death and disability, returning the employee to work as soon as is feasible within the bounds of good health and work capability. This service is far more complex than simply suturing a laceration or performing a preplacement physical examination. The complexities of this practice are complicated by strong regulatory and legislative influences potentially involved with the practice. Physicians have responsibilities that extend beyond the usual clinical situation. A comprehensive program will provide many of the services listed in Table 21-5 (12). There are many settings and situations in which these services are provided. These range from the office of a family physician to acute care clinics, including multispecialty group practices, hospital-based services, occupational medicine clinics, corporate medical services, and consulting practitioners. The full list of services cited in Table 21-5 will typically be available only in the larger, more comprehensive programs. The consultant provides a focused service to the aviation industry. Frequently this involves a particular field of expertise, such as toxicology, ergonomics, wellness, or managerial skills, which is available to the industry on a timelimited, but intense, basis. The services of the consultant are usually focused around problem-solving issues and recommendations may include both short-term corrections and long-term solutions. The types of aviation and space industrial sites where workers are employed are listed in Table 21-6.

Disease management Emergency response service Initial treatment of acute nonoccupational illness Periodic health assessments Preplacement examinations Return-to-work evaluations Substances of abuse testing Termination examinations Treatment of work-related injury or illness Special assessments Biologic monitoring Foreign travel Functional capacity evaluations Hearing conservation Prophylactic immunizations Radiography (B-reading) Respiratory protection clearance Spirometry Visual screening Educational services Back school Cardiopulmonary resuscitation training Community education First responder training Hazard communications: ‘‘right to know’’ Vision conservation Consultation services Americans with disabilities act Community health Disability evaluations Employee assistance program Environmental hazard evaluation Epidemiologic studies Expert testimony Health physics Human engineering (ergonomics) Industrial hazard evaluation Industrial hygiene Medical review officer Research protocol development Safety engineering Toxic hazard information service Work-relatedness of disease (causation) Health promotion activities Fitness Health screening Smoking cessation Stress management Substance abuse management Weight reduction and nutrition Administrative services Evaluation of health-related costs Interaction with community physicians Management of workers’ compensation Medical retirement oversight Professional supervision of on-site clinics Program development

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21-6

Industrial Sites where Workers are Employed Aircraft and space vehicle fabrication and repair sites Aircraft inspection and maintenance centers Airline operations at airports Department of Defense aircraft operation centers Federal Aviation Administrations (FAA) operation and test centers Military aircraft logistic centers National Aeronautics and Space Administration (NASA) operational centers Private and general airports

SCOPE OF PRACTICE In 2004, the American College of Occupational and Environmental Medicine’s (ACOEM) executive board approved a document entitled ‘‘Scope of Occupational and Environment Health Programs and Practice.’’ This document provides an excellent summation of the composition and complexities of an occupational medicine practice whether housed in industry, medical centers, and clinic or private offices. It was noted that the role of the occupational physician had expanded in recent years to enhance the productivity of the worker with absent management and increased emphasis on the wellness of the worker. Recently it has been recognized by organizations and regulatory agencies that such trained physicians have expertise in the analysis and development of programs and policies that protect the worker. The doctor may design programs and management health services directed toward defined populations as well as engaging in clinical care of the individual (13). With expansion of the global economy, the American workforce becomes more involved as an integrated member of a global workforce. This requires the physician to understand the needs of the international worker in the local community and ensure that occupational safety and health care in those communities are encouraged toward the best practices. The complexity of the occupational medicine programs in aviation and space requires intellectual and practical skills beyond the clinical arena. Broad-based practices in this industry require professional teamwork and it becomes necessary to enlist and collaborate with the skills and talents of a large number of colleagues in such areas as industrial hygiene, toxicology, occupational health nursing, safety engineering, industrial relations, health physics, engineering, personnel management, biomechanics, law, public policy, and of course health education. Occupational health programs and their practitioners are advancing the field of health and productivity. To accomplish this it is necessary to incorporate a wide spectrum of activities to include occupational health, safety, loss and risk management, absence and disability management, health promotion, disease management, injury prevention, hazard control, and management of health care benefits. A number of these programs are specifically addressed in the following paragraphs.

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THE WORK PLACE ENVIRONMENT Centuries ago, Ramazzini reminded physicians that in order to know the employment circumstances of a worker, one must go to the work site. In aviation manufacturing or flight control operations, the complexities of the work environment can only be understood through direct observation. Recognition, evaluation, and control of hazards posed by chemical, biological, and physical agents, as well as ergonomic stresses and safety risks, require occasional on-site visits. Areas for consideration when providing these services will be discussed further.

Process Descriptions These are necessary for routine repetitive functions and for special projects that include identification of raw materials, description of processing equipment and conditions (such as temperature and pressure), description of work activities involved, and a description of feedstock, product and intermediaries, by-products, and waste.

Hazard Communications A chemical inventory is required by the Occupational Safety and Health Administration (OSHA) as detailed in the Hazard Communications Standard. The inventory must be comprehensive and include components of mixtures and identification of chemical constituents of trade name products, and it must remain current. For each chemical in use, information must include chemical and physical properties, as well as toxicity features of animal and human exposure at levels thought to be safe for occasional and daily exposure. Material safety data sheets (MSDS) are required for each chemical that is used at the industrial site as directed by the Hazard Communications (right to know) regulation. In addition to toxicologic information, there is additional information and other precautions to be observed in handling, storing, and emergency control measures in cases of spills. Names and phone numbers of individuals to contact for additional information or assistance are listed. From a medical information point of view, the MSDS provides instructions to emergency responders on how to initially manage a worker who has been exposed at a high enough level to cause adverse symptoms.

Listing of Employees A list of each employee with consecutive job titles and work assignments as well as some method for identifying potential chemical exposures should be available. Personnel or environmental monitoring of levels of chemicals or physical agents must be recorded and indicate sampling strategies, procedures, and dates. Ideally, there should be a cross-indexing of workers, job titles, work areas, and projects to allow for comprehensive review of potential past exposures. This is frequently needed for comprehensive medical surveillance of employee exposure. It is not uncommon to find similar listing but only for the current job held by the employee. Because of the issue of long intervals between exposure and appearance of adverse health

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effects such as cancer the entire work history combined with exposure history is important.

Reports of Occupational Injury and Illness Such reports are frequently listed in the OSHA 300 Log, a separate listing of injuries and illnesses that occur in the workplace, and identify the injured worker, the circumstances of the injury, and the degree of medical intervention. This record is helpful in identifying workplace problems so that solutions can be identified and implemented. The log is used to notify federal agencies of the occurrence of accidents and injuries. Such data may be used to establish periodic inspections of the workplace by such state or federal entities.

Control Measures For controls to be effective requires interdisciplinary cooperation between medicine, engineering, industrial hygiene, and management. The implementation of control technologies is most effective and economical when they become a part of the original design and installation. Removing the hazard through control procedures is by far the best preventive medicine action. When solvents or other feedstocks are considered, a product toxicologic review of the material before its procurement may lead to a far safer item than trying to institute control measures after the fact.

EMPLOYEE TREATMENT, EVALUATION, AND EDUCATION Employee treatment, evaluation, and education are occupational medicine services that at one time were commonly provided by the employer on site, but have become a part of the ‘‘sizing’’ of American industry and have frequently been outsourced. These types of services, whether in-house or not, have both medical and nonmedical components. Providing treatment for occupational injury or illness is the obligation of the employer. Such treatment should be handled either by on-site medical personnel or be referred. Complicating health care management is the insurance system that exists in all states and federal agencies known as Worker Compensation to be discussed further.

Work Placement Work placement may depend on the nature and extent of limitations of function caused by medical conditions. Evaluation of such limitations when preplacement medical examinations are performed may influence the proper placement of potential employees. The occupational medicine physician needs to become familiar with the Americans with Disability Act (ADA). This federal program was put in place to ensure that an employee is not discriminated against unfairly when seeking a job. Since its implementation in 1992, it has been more precisely defined through the courts.

Medical Surveillance The program of medical surveillance provides information on ‘‘target organs’’ that may be adversely affected by a particular hazard or multitude of unknown agents. Surveillance programs help to assess the adequacy of protective measures. Medical surveillance includes the development of a baseline health inventory followed by periodic reevaluation. Medical surveillance is not intended to be the sole method for control of exposures to such chemicals. Its intention is to be used as a check on control policies and procedures within the workplace.

Epidemiological Surveillance This type of surveillance can help detect possible work-related adverse health effects. Prudence dictates epidemiologic evaluation of health indicators for those worker populations with potential exposures to possible health hazards.

Education Employee and supervisor education that addresses workplace health factors is vital in preventing illness and injury. There are also significant ethical, legal, regulatory, and employee relations reasons for programs to educate the workforce.

Training Employee and supervisor training in proper work practices and in the use of personal protective equipment may be required or appropriate. Special training is frequently necessary for employees to meet the emergency, first aid, and cardiopulmonary resuscitation needs of the facility. In certain situations, the OSHA Hazard Communication Standard requires employee training and education.

Employee Assistance Programs The Employee Assistance Programs (EAP) provides vitally important services for troubled employees and their families. The comprehensive approach, which may include counseling on marital, financial, and interpersonal issues, is generally more effective than simply limiting such intervention to the traditional alcohol and drug abuse problem. Opportunities for self-referral and confidentiality are important program considerations.

Health Promotion Wellness programs dealing with nonoccupational health situations such as smoking cessation, nutrition, fitness, and other lifestyle issues are increasingly important, and their value to both the worker and industry are now well documented (14,15).

PROGRAM ADMINISTRATION Close interaction with company management and employee representatives (union) is essential to provide a properly tailored, workable program of occupational health services.

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Policies and procedures are management tools that are appropriate to the work site and may be developed by the OEM physician with the concurrence and endorsement of the management and the union.

General Liability General liability considerations are important to prevent claims of willful negligence against the practitioner or the company. Meticulous attention to ethics, medical management, communications, and record keeping are the main stays of defense. Malpractice liability applies to the private practitioner and the corporate physician alike, although the circumstances and degree of liability may vary.

Information Management This tool provides the basic information necessary for a successful program. Federal requirements concerning retention of medical data must be understood and observed. For example, radiographs obtained as part of an asbestos surveillance program must be retained and available for 30 years past the termination of the employee. Communications and coordination are required with workers, technical experts, supervisors, management, and other appropriate people.

REGULATORY AND ADVISORY AGENCIES As in many fields of endeavor in which humans engage in an industrial society there are regulations, rules, laws, and policies. In the field of OEM, there are a number of entities at both state and federal level that provide advice, recommendations, training, and research as well as serve as regulatory agencies with police power. An efficient and effective occupational health program must comply with regulations and seek out and use educational and advisory information. A number of these agencies, administrations, and institutes are described in subsequent text.

Occupational Safety and Health Administration The passage of the Occupational Safety and Health Act in 1971 created the OSHA and the NIOSH. The primary regulatory agency for occupational safety and health is OSHA. Its standards have the weight of law throughout the United States and its compliance officers can inspect the workplace at anytime to determine the status of health and safety. If a serious safety violation is found that could result in immediate harm to workers, the establishment can be closed. The agency can use the power of a court order citation or fine to enforce compliance. States may elect to have their own programs and half have done so. The state program must, as a minimum, meet all the regulations and other requirements established by federal OSHA. This is an agency of the Department of Labor and as such develops regulations, which are announced through the Federal Register.

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One of the early standards established permissible exposure limits (PELs) for hundreds of chemicals. To accelerate the standards-setting process OSHA was permitted to adopt as a consensus standard the threshold limit values (TLVs) established by the American Conference of Governmental Industrial Hygienists (ACGIH). In an agreement signed on August 7, 2000 OSHA and the Federal Aviation Administration (FAA) pledged to work together to improve the working conditions of flight attendants while aircraft are in operation. As a first step the two agencies formed teams to review OSHA standards on record keeping, blood-borne pathogens, noise, sanitation, hazard communication, and access to employee exposure and medical records. Previously OSHA enforced standards for maintenance and ground support personnel in the airline industry while the FAA provided assessment of hazards related to flight deck personnel (16). Currently both the OSHA PELs and the ACGIH TLVs are operative. Each year the ACGIH publishes TLVs for chemical substances and physical agents as well as biological exposure indices. This small handbook, which readily fits into a briefcase, makes readily accessible many of the hazardous exposure levels that should be avoided in the workplace. The nature of the standards-setting process makes the modification of current or the introduction of new PELs extremely cumbersome. The altering or adding new TLVs, although discussed and at times controversial, is far more expeditious and therefore may represent the more current scientific thought. To add further complication to these values is the NIOSH recommended exposure values (REVs). These levels are believed to be low enough that they would constitute levels with no adverse health effects for any worker.

National Institute for Occupational Safety and Health NIOSH is an arm of the Department of Health and Human Services and is housed at the CDC. Like OSHA, NIOSH has the authority to conduct inspections and to question employees and employers and even to include the use of warrants to acquire information on workplace conditions. However, it is not a regulatory agency and cannot levy penalties and this fact enhances its ability to serve as a consultant. Further, it serves the occupational and environmental health community as an educational resource providing not only material but also financial support for educational programs such as residencies in occupational medicine. Funding support is also provided to research projects in the field of OEM.

Environmental Protection Agency The Environmental Protection Agency (EPA) was created to enforce the Toxic Substance Control Act (TSCA) as well as other regulatory functions. It is responsible for regulating the quality of water and air and addresses numerous environmental problems such as hazardous waste sites. When it comes to the workplace, EPA must take a backseat to OSHA until hazardous waste, air or water pollution, or other

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hazardous substances leave the plant site. The EPA works with other agencies in serving as an educational and training source as well as collecting and disseminating information on hazardous materials. Like OSHA, EPA is a regulatory agency and has all the powers necessary for enforcement. Assisting EPA in the same way that NIOSH provides recommendations for regulatory activity to OSHA is the Agency for Toxic Substances Control Registry (ATSDR). Two publications which are the responsibility of ATSDR that are of value to physicians are the ‘‘Toxic Profile’’ series on individual hazardous chemicals and the ‘‘Case Studies in Environmental Medicine’’ series using case studies as a method to educate physicians.

WORKPLACE HAZARDS The aviation industry has the potential of exposing the workforce to numerous hazards that may result in adverse health effects. To assist in the systematic review of the major hazards of concern, they are categorized as chemical, physical, biological, and ergonomic.

Chemical Hazards In many respects, to define a substance as a toxic chemical is redundant. Essentially all chemicals are toxic, given a specific route of exposure or an excessive dose. A gallon of water becomes toxic when inhaled; oxygen can induce convulsions when breathed under hyperbaric conditions; 500 g of table salt taken orally at one setting will have serious adverse effects on metabolism. The topic of toxicology is complex and still evolving. Chemical hazards are harmful substances that may be encountered anywhere in the workplace and have been classified in various ways. Such a classification would include the physical characteristics such as dust, fumes, mist, vapors, gases, and liquids. Another classification can address the chemical class of the hazard and would include acids, bases, solvents, metals, petroleum products, and geologic derivatives such as silica, asbestos, coal, and petroleum. The toxic manifestation of the chemical is related to the steps it undergoes in its interaction with the body. These include uptake, distribution, metabolism, storage, and excretion. To fully understand the toxic manifestations of the chemical, one is required to study these steps in order to understand the adverse effects produced by these interactions. Further information is available in Chapter 9.

Threshold Limit Values The intent of TLVs set by consensus within the ACGIHs TLV committee is to provide reliable benchmarks to aid plant engineers, both in designing new facilities and in renovating old ones, so that the possibility of toxicity occurring in the workforce is minimized (17). In this way, other protective measures such as personal protection, limiting exposure time, and special-purpose occupational medical examinations and tests could either be minimized or better still, documented as

being unnecessary. The basic premise involved in industrial hygiene controls below a permissible (safe) exposure level is that repeated exposures over an 8-hour day, 5 days a week for a working lifetime of approximately 40 years could be allowed for most unprotected employees without harm. Although a few susceptible individuals in the workforce might develop evidence of harm, these persons would be detected by close occupational medical surveillance and removed or protected from further exposure before sustaining irreversible impairment or disability. The individuals who are sensitive or allergic to the chemical in question fall outside the proposed permissible limit, as there may be no safe limit. Unfortunately, the facts that would help place matters of environmental and occupational health into proper perspective are not being communicated adequately to many of our citizens. As a result, a climate exists now in which the adverse effects on productivity and the economy are disregarded while sensationalistic, science fiction–type coverage in the media of environmentally induced illness claims are encouraged and even rewarded. The concept of absolute assurance appears to be the rule that it is reasonable to expect absolutely no risk to the individual, the community, or to the environment from activities of commerce. This tendency toward zero-exposure levels for many chemicals is cost prohibitive and may be without scientific merit. The attitude of some that industries must prove the nonevent, that is that a chemical is absolutely safe, violates the established and well-recognized limitations of epidemiology. There needs to be greater assurance that appropriate instruction in environmental and occupational health occurs at all levels within the biomedical community. For more information on toxic chemicals and toxicology generally, the reader is referred to Chapter 9.

Biological Monitoring Where environmental surveys cannot document adequacy of hazard control below a limiting federal standard (usually half the PEL), special purpose occupational medical examinations and biological monitoring may be required, even if proper protection is worn. Biological monitoring, for example, is required when there is asbestos or benzene exposure beyond the regulated levels. Conversely, where environmental data confirm the adequacy of hazard containment, only a preplacement baseline value may need to be established. To accomplish biological monitoring on a routine basis in the absence of potential hazardous exposures is unjustified due to the administrative burden, the cost of the tests, and the deviation of the worker away from his or her task.

Physical Hazards Physical hazards are defined by Wald as hazards that result from energy and matter, and the relationship between the two (18). Operationally, these hazards as they exist in the workplace can be organized into worker–material interfaces, the physical environment, and energy and electromagnetic radiation. Each of these is present in the aviation industry. Physical agents are formless and essentially weightless, but

CHAPTER 21 Engineering and physical sciences Mathematics

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Biologic sciences Chemistry

Anatomy

Behavioral sciences Physiology

Sociology Psychology (Clinical, industrial and experimental)

Biochemistry

Statistics

Work physiology Time and motion study

Anthropology Anthropometry

Systems safety Information theory Biomechanics

Ergonomics Occupational applications

Manufacturing engineering Industrial engineering Biotechnology Systems engineering Human factors Product design

Occupational medicine (Aerospace medicine, Submarine medicine, Industrial hygiene and safety)

FIGURE 21-1 Disciplines in ergonomics. (From Zenz C, Dickerson OB, Horvath EP, eds. Occupational medicine, 3rd ed. St. Louis: Mosby-Yearbook, 1994.)

may produce hazards to exposed workers by the transfer of energy of various types, resulting in rather specific bioeffects when permissible occupational standards are exceeded. Among the most important potentially harmful physical agents where there is a transfer of energy are (a) oscillatory motions, including noise and vibration; (b) extreme occupational temperature variations in the ambient environment; and (c) ionizing and nonionizing electromagnetic radiation. Figure 21-1 introduces other forms of physical hazards on the job that are typically defined as ergonomic or biomechanical but also have important consequences to worker health, safety, and productivity (19). Many of these hazards are discussed in detail in other chapters within this text (see Chapters 4, 5, and 7).

Electromagnetic Radiation Hazards The electromagnetic radiation hazards (EMRs) spectrum encompasses an unbroken series of ethereal waves, moving with the velocity of light that vary widely in wavelength from cosmic rays as short as 4 × 10−12 cm to hertzian waves (used in radio and power transmission), which extend several miles in length. For purposes of hazard evaluation and control, EMR falls into two distinct categories based on the ability to dissociate a substance in solution into its constituents or ions. These categories are universally identified as ionizing radiation (IR) and nonionizing radiation (NIR). For further details on these hazards in the aerospace environment, the reader is referred to Chapter 8.

Biological Hazards Biological hazards may cause illness as a consequence of their infectious or toxic properties or because they may act

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as antigens and produce an adverse immune response. Such hazards are uncommon in airframe manufacturing, but of major concern in flight line operations. A noted exception in manufacturing is biological agent contamination of machine cutting fluids that are used to disperse heat and assist in removing metal cuttings. In 1960, the first Report and Guide to Hygiene and Sanitation in Aviation was published. This addressed many of the flight line operational issues related to biological hazards. Disposal of passenger-generated waste presents a potential infection hazard to ground personnel. Animal transport by air introduces the possibility of spread of zoonoses to airline and ground personnel. The aircraft as a vector for disease transmission is addressed in Section Two of this chapter.

Ergonomic Hazards Ergonomics has been defined by Chaffin as the science of fitting the job to the worker (20). In both flight line operations and aircraft manufacturing, this interaction of workers with machines focuses on the one hand with compatibility of the worker’s capabilities and limitations, and the job requirements and machine interface on the other. Ergonomic design is well appreciated in the cockpit, but may receive little consideration in engineering the job of a millwright in a cutting machine operation or the biomechanics of baggage handling for ground personnel. Ergonomic hazards are defined as physical stressors and environmental conditions that pose a potential risk of injury or illness to a worker. These physical stressors are described as repetition, force, posture, and vibration. To these stressors must be added the issues of poor job design; inadequate workstation layout; and negative work organizational factors such as work rates, shift work, work-rest cycles, and managerial insensitivity. Human-related error counts for approximately 70% of all transportation accidents including aviation. Fatigue is a significant factor that contributes to human error in the industry. The Air Transport Association (ATA) has developed an alertness management guide to assist those in industry in managing, preventing, and providing countermeasures to operational fatigue. In December 2000, the ATA established an Alertness Management Initiative Scientific Advisory Board to address alertness in flight operations (21). Disregarding ergonomic factors can lead to work related injury and disability. Assembly-line work that requires a repetitive cycle of less than 30 seconds is associated with upper extremity musculoskeletal injury. The application of poor body mechanics to lifting, pulling, or pushing is a major contributor to low back pain and disability. The significant increase in carpal tunnel syndrome over the last 20 years has been attributed in part to repetitive injury and biomechanical strain. In 1985, NIOSH released its Proposed National Strategy for the prevention of workrelated musculoskeletal injury (22). This documented the need to control work-related low back injuries as a national goal. One of the resulting strategies was the development of new lifting guidelines. This effort led to the development of

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the revised 1961 Lifting Equation for Material Handling (23). In 2000, OSHA promulgated a new standard for ergonomics that had been in preparation for nearly a decade. Within months of its publication and before its implementation, it was rescinded by Congress. To date (2007), a new ergonomics standard has not been forthcoming. Currently OSHA has a four-prong approach approved to address ergonomic issues as follows: 1. Guidelines that are developed for specific industries. 2. Inspections for ergonomic hazards with citations issued under the general duty clause. 3. Outreach and assistance to employers for program development. 4. Formation of a national advisory board To determine ergonomic risk, it is helpful to perform a job analysis that evaluates job requirements and psychophysiologic variables, as well as environmental factors. This is the hallmark of prevention: anticipating risks, validating the degree of risk, and then modifying or reducing the risk to avoid biomechanical injury.

OCCUPATIONAL MEDICINE CASE STUDIES FROM THE AEROSPACE INDUSTRY Since the period of World War II in the mid-20th century, numerous occupational and environmental health studies were conducted in the aerospace industry. A number of these studies are reported to provide the reader with examples of occupational hazards at play in this industry.

Jet Fuel Jet fuel is currently used by the U.S. Air Force in most of its inventory of aircraft and in some of the military vehicles and auxiliary ground equipment found at air force bases. Consequently, all operational personnel encounter some level of exposure to jet fuel whether through direct occupational exposure or through incidental contact. Jet propellant-4 (JP-4) was first specified in 1951 as a 50–50 kerosene–gasoline blend. It was the primary U.S. Air Force fuel used between 1951 and 1995. It exists as a mixture of aliphatic and aromatic hydrocarbons and contains a number of additional additives. It is a flammable, transparent fluid with a clear or straw color and a strong kerosenelike smell. More recently, JP-8 has replaced the older fuel type. The transition was complete in 1996 and was due to the need for a less flammable, less hazardous fuel. Both formulations are projected to remain in the inventory until 2025. A commercial aviation version is identified as JET-A. Although JP-8 contains less benzene and less n-hexane, it does have a stronger kerosene smell and an oily feel to touch. Recently developed technology was used to collect samples of exhaled breath from various groups of military personnel. These samples were analyzed in the laboratory for the presence of constituents of the jet fuel. Through the breath

analyzing techniques, investigators were able to quantify human exposure levels and included inhalation, dermal, and ingestion exposures. This jet fuel is similar to commercial international jet fuel A-1. The results demonstrated that exposure occurred with all subjects ranging from slight elevations as compared to a control cohort to more than 100 times the control value with those actively exposed in the workplace. Long-term health effects are yet to be assessed (24).

Mortality Study Among Aircraft Manufacturing Workers In 1999, a report detailing mortality among aircraft manufacturing workers was published. The purpose of the study was to evaluate the risk of cancer and other diseases among workers engaged in aircraft manufacturing that were potentially exposed to compounds containing chromate, trichloroethylene (TCE), perchloroethylene, and mixed solvents. The investigation was a retrospective, cohort, mortality study employing standardized mortality ratios (SMRs) between workers and the general population. The study cohort comprised approximately 78,000 workers who had accrued 1.9 million person years of follow-up. The results of this large study following workers for more than three decades provided no clear evidence that occupational exposures at the aircraft manufacturing factory under study resulted in increases in the risk of death from cancer or other diseases. The overall mortality experience was low with all causes of death attaining an SMR of 0.83 and a cancer mortality with an SMR of 0.90 (25).

Aircraft Workers Exposed to Trichloroethylene and Associated End-Stage Renal Disease The U.S. Renal Data System (USRDS) had reported that in 2001 there were 406,081 cases of end-stage renal disease (ESRD) prevalent in the United States and more than 96,000 incident cases. Patients with ESRD have chronic renal failure that has advanced to the point that they require either dialysis or renal transplant to survive. Identification of potential occupational causes of renal failure is difficult because of the complex multifactorial etiology of the disease, time lag between exposure and disease, and the nonspecific nature of the renal histopathology once it advances to the end stage. Hydrocarbon TCE is a major industrial solvent that has been used in numerous occupational settings, particularly as a metal degreaser. In 2006, Radican et al. (26) published the results of a retrospective, cohort study that suggested exposure to hydrocarbons might increase the risk of ESRD. The study compared the risk in exposed versus unexposed workers at Hill Air Force Base for the period 1973 through 2000. However, exposures were not mutually exclusive and the investigation was limited in its ability to draw strong conclusions about risks associated with individual hydrocarbons. The study used data from three sources: a database of former employees at the airbase, mortality data taken from

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the National Data Index, and ESRD incidence data from the USRDS database. The Hill cohort comprised all civilian employees at the aircraft maintenance facility for at least 1 year between January 1, 1952 and December 31, 1956. The cohort included 14,155 workers of both genders of which approximately one half had been exposed to TCE. As an estimate of intensity of exposure, a cumulative exposure score was generated for TCE that considered individual subjects based on frequency, duration, calendar period of use, and years of exposure. For the time period 1973 through 2000, there was an approximate twofold increased risk of ESRD among workers exposed to TCE, trichloroethane, and JP4 gasoline compared with unexposed subjects all significant at less than 0.05 (26).

Mental Health Outcomes in F111 Maintenance Workers Replacing Fuel Tank Seals In 1973, the Australian Air Force obtained the F111 aircraft. In subsequent years, there was a need to replace fuel sealant material as the F111 does not have a dedicated fuel bladder but instead the fuel occupies the empty spaces between other structures and the shell of the aircraft becomes a giant integrated fuel tank. This design clearly required some form of effective sealant to ensure that surfaces and internal structures did not pose fuel leak problems. In Australia, four fuel tank repair programs ran for over two decades from 1975 through 1999. Each involved different processes and used a range of approximately 60 hazardous substances, mainly organic solvents. In conducting reseal operations, workers would frequently spend extended periods, sometimes up to 5 hours inside the fuel tanks in conditions that were cramped, inadequately ventilated, hot, and with poor communication capacity. Such work was suspended in January 2000 as an initial investigation revealed that the current spray seal process generated symptoms consistent with solvent exposure in the workers. Health effects were assessed in a sample of 105 individuals. A total of 47% of these reported some neurologic/psychological symptoms. These included anxiety/stress, claustrophobia, depression, indecisiveness, irritability, mood swings, paranoia, loss and/or lapses of memory, psychological problems, exhaustion, headache, and head pain. This led to a formal retrospective cohort study to evaluate the possible association between the sealant operation and adverse health status. The study involved mailed questionnaires in addition to a series of clinic assessments with consenting participants. In addition to workers exposed to the sealant operation, two other comparison groups not involved in this kind of exposure were used. Of a total of 872 exposed 592 or 68% consented to participate. The nonexposed cohort consisted of 980 personnel. The results of this epidemiologic study found a consistent and robust association between participation in sealant operational activity and poorer mental health, particularly depression and anxiety, as measured by standardized modules, physician diagnosis, and medication use (27).

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Airborne Polycyclic Aromatic Hydrocarbons at an Airport Polycyclic aromatic hydrocarbons (PAHs) are a group of ubiquitous organic substances made up of hundreds of compounds that include mutagens and carcinogens. Populations may be exposed to PAHs by inhalation of environmental air polluted by the emissions of petroleum-fueled engines or natural sources. Although data on occupational exposure to PAHs are available for many work categories, the literature provided no information concerning occupational exposure to airport staff. Exposure to these workers may be caused by emissions from motor vehicles in use around the airport or from aircraft exhausts. The aim of this study, conducted at an Italian airport, was to measure concentrations of 25 congeners, including biphenyl, by means of a sampling method able to separate vapor and particle-bound fractions of PAHs. Sampling was performed in January and February 2005 at fixed points around the airport that included the baggage area where transport vehicles unload to conveyor belts, a runway with heavy plane and motor vehicular traffic, and the departure lounge. Twelve 24-hour air samples were taken. Although the PAH levels were generally low, higher levels of naphthalene and biphenyl were found. Of more concern was the increase found in levels of benzofluoranthane and benzopyrene (28).

Advanced Composites Recognizing that military aircraft contain advanced composite materials as well as fiberglass, a study was conducted at McClellan Air Force Base to determine the most effective engineering control for dust and fibers generated during advanced composite and fiberglass repair operations. Composite materials that were tested consisted of reinforced fiber and a resin. The fibers within composites are the load-bearing elements while resin molecules fill the voids and transfer the stress from fiber to fiber. The field studies demonstrated that a movable exhaust hood with flexible ducting provided the best control of contaminants generated during repair operations (29).

WORKERS’ COMPENSATION At the end of the 1800s in Great Britain and beginning in the first decade of the 20th century in the United States, a social concern arose for the plight of the worker injured or made sick because of his employment. When a man could no longer, for whatever reason, earn a living he might become destitute and his family wards of society. State by state legislation was introduced that provided protection to the worker and his family should the cause of his impairment be his work. Industry was forced to provide for this worker and workers’ compensation became a mature insurance plan with three components. The first component was to assure that the injured worker received prompt and proper medical care with no personal expense. The second component provided some protection for short-term wage loss resulting

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from the inability to work. The third component provided financial relief with monetary reimbursement should the worker sustain a permanent impairment due to the loss of or the loss of use of a body part or a sensory function such as vision. In the United States currently there are separate workers’ compensation systems in each of the 50 states and numerous systems within the federal government. For example, within the military services, the member is provided medical care and the service pay continues. If retired for medical reasons related to service, the member receives ongoing long-term care from the Veterans’ Administration and may qualify for a medical pension. If a civilian works for a government entity such as National Aeronautics and Space Administration (NASA) or the Department of Defense, the Department of Labor manages the workers’ compensation program. Because of the wide variety of workers’ compensation systems, a common concern for occupational medicine services provided to the airline industry, whether it be in manufacturing or airline operations, is the management of the workers’ compensation system. For the airlines, as a transportation industry, operating in multiple states and across international borders, the management of various components of workers’ compensation is frequently involved, complex, and complicated by an enormous governmental bureaucratic system. Airframe manufacturers may have similar concerns as they frequently have multistate operations. As workers’ compensation is a no-fault insurance program with ‘‘first dollar pay’’ for medical expenses it represents a major cost to the employer. In both state and federal systems, the workers only legal remedy for most job-related accidents or illnesses is through this system. There is reasonable assurance that the worker will receive medical care at no cost, will receive partial reimbursement for lost wages after a minimum qualifying period, and should there be permanent impairment or disability resulting from the job-related injury or illness will receive proportional compensation. At the same time, the employer is spared the inconvenience and expense of lawsuits for injuries occurring on the plant property. Coverage is for all employees including flight crew and ground personnel. To reduce the bureaucratic morass with each state having an independent system, a solution achieved by several airlines through labor negotiations involves identifying a single state that will always have jurisdiction regardless of the geographic location of the incident, or the party may be able to file at the home base location regardless of where in the world the injury occurred. The management and administration of workers’ compensation should assure fairness, encourage appropriate medical management, early recovery, and minimize financial loss to both the worker and the employer. An alternative duty (light duty) policy is a critical element for success in effectively returning the worker to the workplace. Laws and procedures that vary significantly can be major sources of frustration to all. In 1996 the Public Law 104-191: Health Insurance Portability and Acceptability Act (HIPAA) was passed. This

law gave patients the right to protect their health information. This applied to health care providers, institutions, and insurance providers. In most jurisdictions, if the patient (worker) files for workers’ compensation insurance the privacy protection provided by HIPAA may be waived. If providing care or managing such programs, the OEM provider must be knowledgeable of the intricacies and application of this law.

THE AMERICAN COLLEGE OF OCCUPATIONAL AND ENVIRONMENTAL MEDICINE The college was originally founded in 1916 and is the nation’s largest medical society dedicated to the promotion of health of workers through preventive medicine, clinical care, research, and education. The association comprises 31 component societies in the United States and Canada whose members hold scientific seminars and meetings. The college sponsors the annual American Occupational Health Conference in the spring and is the nation’s largest conference of its kind. In the fall, there is the State-of-the-Art Conference that meets in a smaller venue and conducts a more rigorous update of the science of occupational and environmental medicine. ACOEM publishes the peer-reviewed Journal of Occupational and Environmental Medicine as well as a number of other communication pieces. These activities promote the mission of the college that includes educating health professionals and the public, stimulating research, enhancing the quality of practice, guiding public policy, and advancing the specialty. As an international society, ACOEM is the world’s largest such professional organization with more than 5,000 occupational medicine physicians. In 1998, the ACOEM board of directors identified a spectrum of competencies that formed the basis of the practice of the specialty. Although this list does not specifically define a ‘‘core set’’ but rather defines a ‘‘menu’’ that is more reflective of the wide variety of interests and activities of physicians practicing occupational and environmental medicine. This menu builds upon a foundation of general clinical competencies to which are added education, experience, and interest. Another recent development made by the college is the development of the Occupational Medicine Practice Guidelines that is now in its second edition. The guidelines provide high-quality, evidence-based recommendations for patient management. Another document that was developed by the college’s board and has undergone several revisions is its Code of Ethical Conduct. A discussion of ethics concludes this section.

ETHICS For whom does the occupational medicine physician work? That is the question that each physician must not only ask but also answer when entering the field of occupational medicine. It must be realized that the simple answer, ‘‘the

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patient,’’ may not always be appropriate. For example, the recommendation to halt a manufacturing process because it may have high risk to a worker but may cost the job raises the question: does that serve the worker? Is the job applicant upon whom you perform a preplacement examination ‘‘a patient?’’ Is making a recommendation regarding fitness-to-work best serving ‘‘the patient’’ when you have no idea what the duties of the job entail? Do you have a professional, ethical, or moral obligation to the employer who may be paying your salary or the bill? Ethical issues frequently arise in occupational medicine practice because of competing interests, economic issues, regulatory requirements, and organizational power structures. In defining ethics, Rest describes what it is not before indicating what it is (30). Ethics is neither law nor social custom; it is not personal preference or consensus. Rather she holds that ethics is a guide for action that is consistent to held values, principles, or rules that are able to withstand close moral scrutiny. In 1993, the ACOEM, revised its Code of Ethical Conduct and has subsequently reviewed and confirmed the code on several occasions (31). These standards are intended to guide occupational medicine physicians in their relationship with the individuals they serve: employers and workers’ representatives, colleagues in the health profession, the public, and all levels of government including the judiciary. Physicians should: 1. Accord the highest priority to the health and safety of individuals in both the workplace and the environment 2. Practice on a scientific basis with integrity and strive to acquire and maintain adequate knowledge and expertise upon which to render professional service 3. Relate honestly and ethically in all professional relationships 4. Strive to expand and disseminate medical knowledge and participate in ethical research efforts as appropriate 5. Keep confidential all individual medical information, releasing such information only when required by law or overriding public health considerations, or to other physicians according to accepted medical practice, or to others at the request of the individual 6. Recognize that employers may be entitled to counsel about an individual’s medical work fitness, but not to diagnoses or specific details, except in compliance with laws and regulations 7. Communicate to individuals and/or groups any significant observations and recommendations concerning their health or safety 8. Recognize those medical impairments in oneself and others, including chemical dependency and abusive personal practices, which interfere with one’s ability to follow the principles mentioned earlier, and take appropriate measures Professionals of good conscience may differ in the interpretation of such guidelines. The long-term focus should not be on the differences but rather on the continuing

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dialogue that helps to craft refined definitions that meet the expectations of a widening circle of professional colleagues, workers, and employers.

SECTION TWO: ENVIRONMENTAL AND PUBLIC HEALTH ASPECTS OF AEROSPACE MEDICINE Thank God man cannot fly, and lay waste the sky as well as the earth. —Henry David Thoreau

ENVIRONMENTAL MEDICINE Aircraft operate within an atmospheric environment that can potentially pose a host of hazards to crew and passengers. The aircraft hull creates a closed microenvironment that is susceptible to concentrating physical, chemical, or biological hazards. Over the last 20 years, there has been growing awareness of the potential effects aviation may be having on the atmospheric environment. Additionally, the explosive growth in the aviation industry to commonplace occurrence has resulted in significant implications for public health, especially in the realm of communicable disease transmission. The high-density occupancies and proximity between passengers innate to commercial aircraft have implications for contact, droplet, airborne, and vector borne disease modes of transmission. The specialty of environmental medicine focuses on the causes of disease and injury in an environmental context and explores the interactions between environment and human health. As the specialty relates to aviation, this section will discuss environmental issues related to the aircraft cabin, the impacts of aviation on public health, and finally, the impact of aviation on the surrounding community and global environment.

AIRCRAFT CABIN ENVIRONMENT As was made apparent in earlier chapters of the text, aerospace vehicles operate in environments quite hostile to their human occupants. Faced with a cold, hypobaric, hypoxic, and potentially ozone-contaminated flight corridor, aircraft are challenged with providing a microenvironment suitable for the health and comfort of crew and passengers. Hazards, either brought in from outside the aircraft or generated from within the cabin, have the potential to concentrate to levels detrimental to crew and passenger health. Passengers and crew themselves can be the source of cabin contaminants in the form of bioeffluents, viruses, bacteria, fungal spores, and various allergens. As air travel has burgeoned into a commonplace means of mass transportation utilized by 1.5 billion people, there has

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been much written in the trade, lay, and scientific literature on aircraft cabin comfort and air quality (32). Akin to two people in a room disagreeing over it being too warm or too cool, the perception of comfort in an aircraft can be as varied as the number of people onboard. Passengers and cabin crew frequently complain that the air on planes is unpleasant and may be unhealthy (33). Trade and lay publications tend to be less than rigorous in scientifically linking complaints of crew or passenger discomfort to cabin air quality. The scientific literature reports headache, fatigue, and respiratory symptoms among the more common complaints, especially on long duration flights, in which cabin air quality is questioned. A difficulty in interpreting many of these studies is the general lack of health effects data for passengers and crew collected in conjunction with clear exposure information. Therefore, it is difficult to establish a causal relationship between poor cabin air quality and adverse health effects (34). It is also important to note that the literature centers upon cabin air quality under routine operations. Owing to mechanical failure or adverse flight incident, smoke, engine oil, hydraulic fluid, or de-icing solution could be introduced into the cabin, creating a frankly toxic environment for occupants. Two environmental factors that may contribute to complaints about air quality are low relative humidity and pesticide use (Table 21-7). Nagda and Koontz reviewed 21 studies of reported flight attendant health and comfort in airliner cabins published from 1980 to 2000 (35). These studies employed in-flight surveys or general flight experience surveys. In addition, some research included objective measurements of test subjects, such as pulmonary function tests or pulse oximetry. Recognizing shortcomings such as small sample sizes, poor response rates, and response bias, this body of studies illustrates the fact that flight attendants perceive that they develop a host of symptoms related to the airline cabin environment. Frequently reported symptoms include dryness, fatigue, bloating, headache, and earache. It is important to bear in mind that many of the ‘‘air quality’’ studies occurred before the smoking ban.

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Factors Involved in Cabin Air Quality Pressurization Ventilation Recirculation Nonrecirculation Air contaminants Chemical Biological Air filtration Temperature Relative humidity

In the early days of airline operations, the ranks of flight attendants were made up of young women in their 20s and early 30s. Currently, the demographics of this workforce have changed to include much older employees. Actual sensitivity to air quality or the perception that air quality is adequate may have changed with this population at risk.

Physical Factors Environmental control systems must provide a safe and comfortable cabin environment despite cruising at altitudes in excess of 12,000 m. Pressurization, temperature regulation, airflow, and filtration are necessary elements of the aircraft environmental control system. By Federal Air Regulation (FAR), cabin pressure altitude cannot exceed 2,438 m (8,000 ft). The basis for this level was the oxyhemoglobin dissociation curve, given the assumption passengers are healthy, normal individuals and would be capable of maintaining a saturation of 90%. Although this assumption might have been valid when air travel was in its youth, currently the spectrum of passengers is broader, regularly including the sick and elderly. To accomplish a suitably pressurized cabin, air is compressed by the aircraft engines and bled off from one of the compressor stages to the environmental control system. Heated significantly due to the compression (Charles’ law), the air must be cooled by heat exchangers and an airconditioning system to reach a comfortable temperature range (36). Airflow is continuous and laminar, moving side to side across sections of the cabin. This design element is important in understanding airborne communicable disease transmission in aircraft. Fresh cooled air combines with an equal amount of recirculated, highly filtered cabin air. The high-efficiency filtration system captures dust, allergens and other particulates, and most airborne microbes. Odors tend to be quickly diluted due to the continuous airflow, which can provide more than 20 cabin air changes per hour—a generous exchange rate compared to those seen in office buildings. The astute reader may question why half of the cabin air is filtered and recirculated, when it would be entirely possible to provide 100% of the intake air from the compressor duct. In fact, older aircraft employ this very construct because their engine design produces most of its thrust from the engine core. Extracting all of the cabin airflow from the compressor had only modest impact on fuel economy. However, newer designs employ high bypass ratio fans that move most air around the core of the engine instead of through it. Most of the thrust is provided by the bypass air. On this type of engine, tapping air from the engine core significantly decreases fan thrust and impacts fuel efficiency (36). A compromise is struck with partial recirculation in order to balance fuel consumption, environmental emissions, and cabin air quality. Because the inflow air at altitude is very dry, another benefit derived by recirculating part of the cabin air is a modest increase in relative humidity. Relative humidity levels often drop below 5% on long duration flights (33).

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Chemical Contaminants Just as with any indoor environment, an aircraft possesses a variety of sources of volatile organic compounds (VOCs). Painted surfaces, fabrics, and carpets may off gas especially when they are first brought into service. Cleaning products, as well as food being handled and heated, can contribute to cabin volatile organics. The ventilation system is usually free of VOCs because the compressor stage source is taken before air enters the combustion chamber. In the setting of a mechanical failure such as a seal leak, contaminants could enter the ventilation system but would quickly be recognized as an in-flight emergency with odor and probably smoke or fumes in the cabin.

Carbon Dioxide The primary source of carbon dioxide in an aircraft is the respiratory exhalations of the crew and passengers. With adequate environmental control system ventilation, levels of CO2 remain well under concentrations associated with adverse health effects or performance decrement. Subsequently, carbon dioxide levels can be thought of as an indicator of the adequacy of ventilation. Normal outside air at the surface contains approximately 380 ppm (0.03%) carbon dioxide (rising from a preIndustrial Revolution level of 280 ppm). Human ventilation rates increase if the inhaled CO2 concentrations reach 20,000 ppm (2%) and health effects such as dyspnea, dizziness, and slowed mentation would not be expected until approximately 60,000 ppm (6%) (37). FAR 25.831 establishes the FAAs standard for cabin CO2 as 5,000 ppm (0.5%). Air quality studies have not identified high carbon dioxide levels in flight (32). Another potential source of carbon dioxide aboard aircraft is in the sublimation of dry ice used as a refrigerant for perishable goods. In 1998, while taxiing to takeoff, all four crewmembers of a DC-8 freighter became dyspneic (38). Donning oxygen masks, they safely returned to the terminal without incident. The cargo included 960 lb (198 4.85 lb blocks) of dry ice in the main cargo bay to ship frozen shrimp. Following this incident, National Transportation Safety Board (NTSB) asked the FAA to reexamine its maximum dry ice allowance based on cabin volume. Since the original studies on sublimation rates, which demonstrated 1% per hour, dry ice preparations have morphed from 100 lb blocks to small, several pound pellet forms. A subsequent FAA study found the pellet form of dry ice to have a sublimation rate twice as high as the older block form (39). Aircraft volume and air exchange rates are then used to determine a safe limit for onboard dry ice.

Carbon Monoxide Any source of unintentional combustion aboard an aircraft has the potential to introduce carbon monoxide into the cabin. Obviously, the engines are the primary potential source for this serious toxin, but as was discussed previously, it would be unlikely for engine emissions to find their way into the ventilation system without immediate notice. Cabin air

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quality studies have not documented unsafe levels of carbon monoxide under routine conditions. FAR 25.831 establishes a CO cabin limit of 1 part in 20,000 (0.005%). However, small aircraft with reciprocating engines may introduce CO into the cabin through leakage by the heating system.

Ozone Ozone, a triatomic allotrope of oxygen, is a clear blue gas that is naturally formed when ultraviolet (UV) light interacts with stratospheric oxygen. Molecular oxygen photodissociates, freeing an oxygen atom that can combine with another molecule of oxygen to form ozone. Ozone itself can be dissociated by UV light back to oxygen. This oxygen–ozone forming and dissociation cycle has the effect of absorbing solar radiation and heating up the atmosphere. The presence of ozone in the lower stratosphere (LS) and upper troposphere (UT) is essential to life on Earth because of its properties in filtering out harmful UV radiation. It is a potential contaminant aboard aircraft, entering through bleed air at cruise altitudes. Stratospheric ozone concentrations vary according to altitude, latitude, season, and low pressure systems—with levels highest in the northern hemisphere during late winter and early spring. High-altitude military reconnaissance aircraft must routinely deal with this cabin contaminant by staying on supplied air. Ozone is a respiratory irritant with mild exposures leading to eye, nose, and throat irritation, chest tightness, and headache that typically resolve with cessation of exposure. Studies have associated ozone exposure with decreased lung function, exacerbation of asthma, and immune system impairment (40–43). The FAA, in FAR 25.831, has set the standard for cabin ozone at 0.25 ppm (sea level equivalent) at any time above 9,750 m (32,000 ft.) There is also a 3-hour time-weighted average of 0.100 ppm over a 3-hour period when above 8,250 m (27,000 ft.) Studies of cabin ozone level have shown a minority of long duration, late winter/spring flights may exceed the FAA limit (32,44). Some carriers provision their aircraft with ozone converters, which can effectively neutralize this hazard.

Allergens As with any indoor environment, particulates of dust, pollen, fibers, hair, and hair products may be present in the aircraft. Passengers allergic to such substances benefit by new air being constantly introduced into the cabin and particulates being trapped by high-efficiency particulate atmosphere (HEPA) filtration. Passengers with severe food allergies may be at risk if the food is served and consumed by fellow occupants, although exposure through inhalation or contact tends to lead to less severe reactions.

Communicable Disease The influence of air travel and infectious disease spread has been the subject of investigations for many years. The International Civil Aviation Organization (ICAO) forecasts that by 2015 more than 2.5 billion people will travel by air each year. The potential impact on the spread of infectious

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disease may be substantial, for example, discussions of a possible avian influenza pandemic invariably include the role of air travel in exacerbating spread (see Chapters 19 and 28 for additional information). During a recent investigation of travel-related severe acute respiratory syndrome (SARS), patients meeting the case diagnosis of cough, difficulty breathing, and fever, plus a close contact with a SARS patient or stay in an area with epidemic SARS, had respiratory samples tested by polymerase chain reaction. Thirty percent of samples were positive for influenza or parainfluenza virus (45). Minority percentages (all 500 DU

FIGURE 21-3 Satellite sensor data demonstrating distribution of global ozone concentration in mid January. OMI, ozone monitoring unit; CSFC, Commitee of State Financial Control. (Courtesy of NASA.)

by atomic chlorine and bromine. The main source of halogen atoms in the stratosphere is from surface release of chlorofluorocarbon compounds and bromofluorocarbon compounds. Although these compounds are heavier than air, they work their way up to the stratosphere and photodissociate into chlorine or bromine atoms. (The need for light energy explains the seasonal nature of the Antarctic ozone ‘‘hole.’’) If stratospheric ozone decreases, absorption of incoming UV radiation decreases and more of it is able to reach the surface. This becomes especially concerning for ultraviolet B (UVB) wavelengths (270–315 nm). Increased incoming UVB radiation at the Earth’s surface could pose serious biologic effects for the planet. Harm to oceanic plankton, harm to land plants, and increased incidence of actinic skin damage, skin cancers, and cataracts are a few of the possible consequences of ozone depletion. Jet engine emissions produce a number of chemically active species that have the potential to affect atmospheric ozone concentration. According to the IPCC, a scientific panel established by the World Meteorological Society and United Nations Environment Programme, engine emission species having the greatest potential impact are nitrogen oxides, sulfur oxides, soot, and water. In the troposphere and LS, ozone concentrations increase in response to oxides of nitrogen and decrease in response to water and sulfur. Although soot particulate has the capacity to decrease ozone, the emitted concentration of soot is so low; this property is not thought to be significant. Unlike halogen atoms, soot particles do not propagate a catalytic destruction of ozone. At the upper levels of the stratosphere, ozone concentrations decrease in response to oxides of nitrogen. Aircraft emissions are believed to have increased the concentration of oxides of nitrogen at cruise altitudes in the northern mid-latitudes by 20%. This change is not as

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dramatic as it first sounds when considering the variability observed in atmospheric NOx and the vertical movement of nitrogen oxides. Jet engine NOx emissions are small compared to fossil fuel burning at the surface and oxides of nitrogen are additionally formed naturally by lightning in the troposphere. In its 1999 report titled ‘‘Aviation and the Atmosphere’’ the Intergovernmental Panel on Climate Change states: ‘‘In summary, because the database for ozone observations in the UT (upper troposphere) and LS (lower stratosphere) is still relatively limited and because uncertainties in observational data, as well as model representations of non-aircraft ozone forcing phenomena, are quite large, it is presently impossible to associate a trend in ozone to aircraft operation with meaningful statistical significance.’’

Understanding ozone depletion has required a great deal of work in unlocking the complexities of atmospheric chemistry—leading to at least one Nobel Prize. Appreciating the true impact aviation may have on this subject will need to wait for future editions of this textbook.

Alternate Fuels Current jet fuels are a blend of hydrocarbon saturates, aromatics, and various additives. Although there are differences in specifications across the spectrum of civil and military fuels having to do with a desired freezing point, flash point, thermal stability, or volatility, all are nevertheless kerosenetype refined petroleum products. Although the price of jet fuel is tied to the crude oil market, it has risen disproportionately over the last several years, making fuel cost the largest operating expense for U.S. airlines (73). In the short term, there are concerns over volatility in the petroleum market related to geopolitical forces. In the longer term, as petroleum consumption continues to climb, global supply capacity may be overtaken by demand. Initiatives striving to develop alternatives to traditional crude oil–based jet fuel will need to deal with operational, financial, and environmental consequences. Biomass conversion and coal-derived fuel are examples of potential alternatives. However, any proposed alternate fuel source will need to be assessed against the balance of properties currently afforded by kerosene-type fuel. Energy density, safety, operational issues, cost, and emissions differ significantly across potential fuel candidates.

Noise Noise is the term we apply to any unwanted sound or sound pollution. It is an important issue both occupationally and environmentally. Noise is an unfortunate, yet fundamental characteristic of aircraft operations. Turbojet, turbofan, turboprop, and piston engines all generate considerable noise levels. This noise is especially problematic near takeoff and landing patterns. Cities have had to make choices of placing their airports at locales close enough to conveniently serve the intended population versus keeping them in relatively remote areas to mitigate unwanted noise. Even in cases in

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which airports were built away from dense population areas, urban sprawl has in many cases eventually brought the city to the perimeter of the airport. Additional information may be found in Chapter 5.

Noise Measurement Sound is our perception of acoustic energy. Owing to the large range of acoustic wave amplitude the ear is capable of hearing across; it is useful to employ a logarithmic decibel amplitude scale. With such a scale, a 20-dB noise level is ten times greater than a 10-dB noise. A 36-dB sound is twice as loud as a 33-dB sound. If a machine generates 62 dB of noise, turning on two such machines would be expected to generate 65 dB. A typical conversation is approximately 60 dB. When we are around noise loud enough to compel us to shout to converse with someone approximately 3 ft away, we are approaching 85 dB, which is defined as hazardous noise. Prolonged exposure to noise levels exceeding 85 dB can permanently damage the ear and cause sensorineural hearing loss and tinnitus. Noise Effects The effects of noise on physiology and health have been well described in the occupational literature. However, these data cannot be generalized to environmental exposure. There are few quality studies that have analyzed community health effects from aircraft noise. A problematic effect of noise is that of interference with spoken communication—referred to as masking. Social surveys have indicated that aircraft noise interferes with direct conversation, telephone use, radio or television use, and disrupts desired levels of quietness. It probably comes as no surprise that interference with sleep due to aircraft noise generates more hostility and complaints than daytime interruptions. Communities tend to be much more sensitive to noise pollution during traditional sleeping hours, forcing many airports to alter their operations to provide ‘‘quiet hours’’ for the surrounding community. Various composite noise indices have been developed to assess the impact of environmental noise in a community. The first composite noise rating (CNR) was introduced in the 1960s and was designed to evaluate land use near airports and predict annoyance levels secondary to airport operations. The measurement is based on maximum perceived noise level and frequency of day and night flights. Night flights are weighted 10-to-1 over day flights. A newer index, the noise exposure forecast (NEF) was developed by the FAA to predict community annoyance from aircraft operations utilizing an effective perceived noise level and similar weighting as the CNR. The effective perceived noise level takes into account tone components in aircraft noise and noise duration. Parameters such as seasonal corrections (effect of open windows, outdoor activities), outdoor residual noise levels, prior community experience with intruding noise, and pure tone versus impulsive character of noise may be added to the overall analysis. Studies have examined the relation between environmental noise exposure and reading comprehension of children.

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Retrospective studies may point to an effect of chronic noise exposure on reading, but may be confounded by the potential effects of acute noise exposure during testing. A pooled, multinational study reported a linear association between aircraft noise exposure at school and impaired reading comprehension (74). The association was maintained after adjustment for socioeconomic variables and acute noise annoyance. Community surveys have linked aircraft noise to various physiological and psychological complaints. Studies have raised the question of possible associations between environmental aircraft noise and elevated levels of stress hormones and cardiovascular effects such as hypertension.

Noise Governing Guidance The Convention on International Civil Aviation, also referred to as the Chicago Convention, requires all aircraft engaging in international operations to be issued a certificate of airworthiness. Part of that Convention (Annex 16) established standards for the control of aircraft noise. ICAO’s Committee on Aviation Environmental Protection (CAEP) is responsible for environmental aspects of aviation and includes noise and engine emissions. The committee is charged with undertaking studies related to the control of aircraft noise. Two working groups under CAEP deal with the technical and operational aspects of noise reduction and mitigation. Before the committee can approve an increase in certification stringency, it must be able to meet economic reasonableness, technical feasibility, and prove an environmental benefit. Sonic Booms The term sonic boom refers to the air shock an object causes when traveling at the speed of sound. Although purposes of this text will discuss the sonic boom of supersonic aircraft and spacecraft, many other objects (flying or otherwise) are capable of creating this phenomenon. The crack of a bullwhip is created when the whip arc passes down the length of the leather and creates a miniature sonic boom. Thunder is the result of rapid heating and expansion of air due to lightning. As an aircraft flies near the sound barrier, pressure waves similar to those seen around the bow of a boat begin to be forced together due to compression (Figures 21-4 and 21-5). The point at which these leading pressure waves merge into a single shock wave is at the speed of sound, or Mach 1, approximately 1,225 km/hr (735 mph) at sea level. The generated shock wave can yield tremendous sound energy in excess of 200 dB. Sonic booms are not well tolerated by communities and for this reason, supersonic flight is generally not authorized outside special use, for example, military operations areas. Future Solutions for Aviation Noise If a functionally silent aircraft were to be successfully designed and built in 1 day, the impact on airport operations volume, operating hours, and pattern proximity to residential areas could be considerable. The enabling technologies

FIGURE 21-4 Subsonic flight demonstrating compression of pressure waves in front of aircraft.

that would need to be developed would have to mitigate noise generation from the aircraft’s propulsion system as well as that generated from the airframe. Engine design modifications will presumably need to work on reducing the exhaust jet speed. In order to quiet the engine, yet maintain sufficient thrust, the engineering challenge would be to somehow enlarge the engine exhaust area without dramatically compromising on engine size and weight. A joint research venture between Massachusetts Institute of Technology (MIT) and Cambridge is looking at designs that blend fuselage and wings together, optimizing airframe lift. This property could allow for lower power settings in landing

FIGURE 21-5 Mach one flight demonstrating merging of pressure waves into single large shock wave.

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and takeoff phases, thereby decreasing noise generation. Interestingly, the current tube and wing configuration of modern airframes largely came about due to safety concerns for engine fires. A burning engine mounted to a pylon is relatively isolated from the rest of the airframe.

Radiofrequency Radiation Radiofrequency radiation (RFR) is a low energy form of NIR. RFR frequency extends from 3 KHz to 300 MHz and is extensively used throughout the aerospace industry. Microwave radiation is also employed in aviation and is of higher energy at 300 MHz to 300 GHz. Radio beacons, very high frequency omni-directional radio (VOR), and radar systems are examples of aviation-related devices that generate RFR. Although these sources are important to consider in an occupational medicine context, that is a ground crew is exposed to a radar beam when erroneously left on, RFR sources are far less significant when discussing environmental exposures. One reason for this is the fact that RFR field strength drops off rapidly with distance from transmitters. Permissible exposure guidelines for RFR are published by the American National Standards Institute C95.1. The standards are based on whole body exposure, are time weighted (maximum permitted exposure for unrestricted occupancy), and dictate whether areas near a transmitter require restricted entry. There appears to be no significant risk to the general public attributable to aviation-related RFR.

Cosmic Radiation The earth is incessantly showered by IR from space—variously referred to as cosmic radiation, galactic radiation, or cosmic rays. The latter term is rather misleading because cosmic radiation particles arrive individually, not as a beam or ray of particles. Cosmic radiation consists of high speed charged or neutral subatomic particles of various energy levels. The vast majority of particles are protons, followed by α particles and rare heavier nuclei and electrons. Astronomers and physicists believe that the radiation originates from within the Milky Way galaxy from rotating neutron stars, supernovae, black holes, and our own sun (75). The incoming radiation collides with atmospheric molecules and produces lower energy secondary cosmic radiation. As one approaches the earth’s surface, there are increasingly more gas molecules to collide with, eventually providing protection from all but the highest energy particles. For this reason, exposure to significant levels of cosmic radiation would be expected to occur at only the higher altitudes. The incoming rate of cosmic rays onto the upper atmosphere is negatively impacted by the solar wind. Solar activity varies over an 11-year cycle, changing the intensity and expanse of magnetized plasma enshrouding the earth. Rarely, a solar proton event may cause an increase in cruise level radiation to aircrews and passengers. Cosmic rays are also attenuated by the earth’s magnetic field. The lines of force of this field are nearly parallel to the surface of the earth near the equator and nearly perpendicular at the poles. Therefore, flights at higher latitudes can be expected to

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allow higher exposures to cosmic radiation than those in the tropics. The FAA’s Civil Aerospace Medical Institute has developed a computer program, named CARI-6, capable of computing the effective dose of cosmic radiation received by an individual on any particular flight. By inputting the date of flight, origin and destination airports, and involved altitudes, the program takes into account altitude, geographic location, the earth’s magnetic field, and heliocentric potentials (solar activity cycle) then calculates an effective dose for any given flight. The currently employed SI unit for expressing a radiation dose is the sievert. It is numerically related to the previously used roentgen equivalent man (rem) unit in that 1 Sv = 100 rem. The sievert attempts to reflect the biological effects of radiation, as opposed to the physical aspects characterized by the absorbed dose in grays. One important concept in the discussion of cosmic radiation exposure is that of proportionality given other sources of radiation exposure. Owing to terrestrial sources of radiation (radon, uranium), annual doses of IR at sea level could reach 2 to 3 mSv/yr. The commonplace use of diagnostic medical imaging studies further subject individuals to radiation. For example, a standard chest x-ray exposes an individual to approximately 0.1 mSv. Of course, this is a short duration, concentrated dose of radiation compared with the whole body exposure encountered in transoceanic flights diluted over many hours. There are a number of relevant standards for IR exposure limits. The International Commission on Radiological Protections (ICRP) established a standard of 1 mSv/yr for the general public and 20 mSv/yr for nuclear industry workers, averaged over 5 years. A crewmember flying frequently and regularly at high latitudes and high altitudes would be subjected to the greatest annual cosmic radiation exposure. A representative dose equivalent rate from cosmic radiation at cruising altitude might be 5 mSv/hr. The average aircrew annual dose probably lies within 3 to 6 mSv, which is only a few times natural background. If future aircraft designs require significantly higher cruising altitudes (i.e., >21,000 m), health risks due to cosmic radiation may grow in significance. Cumulative cosmic radiation exposure is so low, statistical power becomes a major concern in interpreting the literature. Studies looking at the effects of low-level doses of IR from all sources have centered largely upon cancer risk, although genetic and fetal harm have also been the subject of investigation. Research that has specifically looked for effects from cosmic radiation exposure in flight crews and flight attendants is more limited. When one considers the potential overlay of environmental exposures of aircrews to jet fuel, engine emissions, hydraulic fluid, radar, and so on the subject becomes even more complex. Studies have looked for health effects due to cosmic radiation in military aircrew, airline pilots, and flight attendants (76). Whereas some studies have demonstrated a reduction in the expected incidence of some cancer types, incidence rates of some cancers that include non–melanoma

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and melanoma skin cancer and breast cancer were found to be increased (77–79). Expected versus observed cancer numbers within subgroups of aircrew studies tend to be small—often single digits (80). A large European flight attendant cohort study demonstrated no increased mortality attributable to cosmic radiation (81). A meta-analysis of cancer incidence among female flight attendants looked at cohort studies from 1966 to 2005 and confirmed increased risk for malignant melanoma and breast cancer among female flight attendants (82). Discussions of differences between female flight attendants and the general female population such as nulliparity provide alternative explanations to an occupational exposure (83). Skin cancer tends to appear in higher rates among aircrew and several authors attribute this finding to aircrew lifestyle and a greater opportunity to spend time sunbathing than the general population. A questionnaire by Rafnsson et al. attempted to identify malignant melanoma risk factors among aircrews, but failed to demonstrate identifiable differences between aircrew and the general public (78). Epidemiologic studies provide little consistent evidence linking cancer with radiation exposures in an aviation setting. Additional information may be found in Chapter 8.

Radio Isotope Generators Cosmic radiation and solar events pose even greater potential risk to astronauts, who must operate completely outside the earth’s atmosphere and potentially, outside the earth’s magnetic field. Space radiation is one of the most significant hazards associated with orbital missions and will probably remain so with interplanetary missions. The reader is referred to the section on space environments for review on the subject. Another source of IR to consider is that generated by radioisotope thermoelectric generators. These generators contain plutonium-238 dioxide, which, through radioactive decay, heats a thermocoupler to generate electricity for a variety of spacecraft applications. Decay products are α-particles that are very easily stopped by even light shielding. The ceramic form of plutonium-238 was chosen for its properties of heat resistance, low vaporization, and tendency to not generate dust when fractured. NASA has gone to great length to enclose the plutonium pellets within three layers of protection and tested the system against fire, blast, ground impact, and immersion with good assurance of ruggedness.

Security Scanning Technology has been employed for many years to provide security for aviation. Airport security provides a first line of defense against terrorists bringing weapons or bombs into an airport—greatly reducing the likelihood of such devices being brought onboard an aircraft. Screening of passengers, baggage, and freight tightened significantly after the terrorist strikes of September 2001 in which commercial planes were used as weapons. Metal detectors and gas chromatography for detecting volatile compounds given off by explosives are used routinely at airports. Standard x-ray tube fluoroscopy and computed tomography may be used to screen luggage.

Physical distances, lead curtains, and administrative controls are employed to minimize exposure to radiation scatter. Radiation exposure is not considered a significant exposure to security workers. Risk to passengers or flight crews should be considered trivial. More advanced x-ray machines utilizing backscatter technology are available to provide the equivalent of a strip search for passengers that require additional screening. Backscatter systems construct an image based on how various materials scatter x-ray photons. Organic materials feature much more specific scatter patterns than absorption patterns; therefore drugs and liquid explosives are visualized even if adhering next to body parts. The Health Physics Society estimates that a single backscatter scan delivers 0.00005 mSv to an individual (84). A frequent flyer, who might have to undergo the improbable number of 200 scans in a year, would only reach the negligible dose range of 0.01 mSv formulated by National Council on Radiation Protection and Measurements (NCRP).

ATMOSPHERIC CONCERNS Contrails Contrails are condensation trails that occur at high altitude due to water vapor being introduced by engine exhaust. The cold temperature and low vapor pressure at altitude causes the hot, humid air in the jet exhaust to exceed saturation, condense, and form ice crystals around particulate nuclei. Contrails may play a role in stratospheric and upper tropospheric chemistry. Depending on upper tropospheric winds and relative humidity, the formed contrail may dissipate quickly or persist for hours or more similar to a cirrus cloud. In a NASA satellite study, contrails were shown to last from 7 to 17 hours and some cases enlarge into 12,000 km2 natural looking cirrus fields (85). In heavy air traffic corridors, the presence of large numbers of contrails can significantly contribute to cloud cover, potentially affecting the radiation balance of an area (Figure 21-6). This increased cloud cover both decreases incoming solar radiation (cooling effect) and reduces radiational cooling (warming effect). During the September 11, 20013-day grounding of flights, researchers were able to observe the temperature effect in the absence of contrails. When compared to averaged 30-year historical temperatures across 4,000 weather stations across the continental United States, the days of the grounding demonstrated an average increased diurnal temperature range of 1.8◦ C—that is the lack of contrails appeared to make the days warmer and nights cooler (86).

Fuel Dumping Some aircraft, especially large models optimized for longdistance flights, have a significantly higher maximum structural takeoff weight than permissible landing weight due to fuel storage. In the event the aircraft must land before it has consumed sufficient fuel to reach its landing weight, it

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contribution of Dr. Mark Roberts, Dr. Al Parmet, and Dr. Claude Thibeault, who authored the impact of aerospace industry on environment and public health content in previous editions of this textbook.

REFERENCES

FIGURE 21-6 Satellite imagery demonstrating contrails over heavily traveled corridor in Europe (Photo courtesy of NOAA).

may need to jettison fuel in flight. This is not a routine event. From a purely economic basis, no airline is eager to dump thousands of gallons of jet fuel into the air. The development of a mechanical problem or passenger problem might force the flight to return to the airport or divert to another airport short of the destination. Fuel dumping procedures are addressed in the FAA’s Aeronautical Information Manual under emergency procedures and require coordination with Air Traffic Control (ATC). When a pilot decides to dump fuel, ATC broadcasts the event to area aircraft (87). VFR aircraft must clear the affected area and IFR aircraft are provided vectors to clear the area as needed. The aircraft jettisoning fuel is assigned an altitude at least 2,000 ft above the highest obstacle within 5 mi of route to ensure maximal evaporation (88). Studies have looked at the fate of jettisoned fuel and have characterized droplet formation and evaporation. In ambient temperatures above freezing, fuel dumped above 1,500 m evaporates nearly completely—that is greater than 98% (89). In tests where fuel was jettisoned as low as 750 m at temperatures approximately 11◦ C, no liquid fuel could be detected by ground observers and sampling detected concentrations at only a few ppm (90). Any remaining fuel droplets and vapor are widely dispersed by atmospheric movement and turbulence, rendering hydrocarbon densities too low to create any perceptible environmental effect. In ground studies, obviously more applicable to fuel spills, there is ample evidence that jet fuel is biodegraded in soil.

ACKNOWLEDGMENTS The authors were ably assisted in the production of this chapter by Ms. Jean Coppin. We wish to recognize the

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49. Moser MR, Bender TR, Margolis HS, et al. An outbreak of influenza aboard a commercial airliner. Am J Epidemiol 1979;110:1–6. 50. Brownstein JS, Wolfe CJ, Mandl KD. Empirical evidence for the effect of airline travel on inter-regional influenza spread in the United States. PLoS 2006;3(10):1826–1835. 51. Olsen SJ, Chang HL, Cheung TY, et al. Transmission of the severe acute respiratory syndrome on aircraft. N Engl J Med 2003;349:2416–2422. 52. Vogt TM, Guerra MA, Flagg EW, et al. Risk of severe acute respiratory syndrome-associated coronavirus transmission aboard commercial aircraft. J Travel Med 2006;13:268–272. 53. Public Broadcasting System. NOVA Archives, The most dangerous woman in America, the history of quarantine. http://www.pbs.org/ wgbh/nova/typhoid/, accessed March 2007. 54. World Health Organization. Revision of the International Health Regulations. available online at http://www.who.int/csr/ihr/ IHRWHA583 en.pdf, accessed February 2007. 55. Baker MG, Fidler DP. Global public health surveillance under new international health regulations. Emerg Infect Dis 2006;12(7). 56. Eisenberg MS, Garrslev K, Brown W, et al. Staphylococcal food poisoning aboard a commercial aircraft. Lancet 1975;2(7935):595–599. 57. Tauxe RV, Tormey MP, Mascola L, et al. Salmonellosis outbreak on transatlantic flights; foodborne illness on aircraft: 1947–1984. Am J Epidemiol 1987;125(1):150–157. 58. Hedberg CW, Levine WC, White KE, et al. An international foodborne outbreak of shigellosis associated with a commercial airline. JAMA 1992;268:3208–3212. 59. CDC. Cholera associated with an international airline flight, 1992. MMWR Morb Mortal Wkly Rep 1992;41:134–135. 60. CDC. Update cholera—western hemisphere, 1992. MMWR Morb Mortal Wkly Rep 1992;41:667–668. 61. World Health Organization. Report of the informal consultation on aircraft disinsection. Report WHO/PCS/95.51. Geneva: WHO, Nov. 610, 1995. 62. Kozarsky P, Arguin P, Navin A. Conveyance and transportation issues: air travel, including disinsection. In: Travelers’ health: yellow book, health information for international travel, Centers for Disease Control and Prevention. Mosby, 2005–2006. 63. Gratz NG, Steffen R, Cocksedge W. Why aircraft disinsection? Bull World Health Organ 2000; 78(8). 64. Das R, Cone J, Sutton P. Aircraft disinsection. Bull World Health Organ 2001;79(9):900–901. 65. Kilburn KH. Effects of onboard insecticide use on airline flight attendants. Arch Environ Health 2004;59(6):284–291. 66. Rayman RB. Aircraft disinsection. Aviat Space Environ Med 2006;77:733–736. 67. Airport malaria in Luxembourg. Case report by Robert H. Euro Surveill 19 August 1999;3(34):1. 68. Conlin C, Berendt AR, et al. Runway malaria. Lancet 1990; 335(8687):472–473. 69. Intergovernmental Panel for Climate Change. Special report: aviation and the global atmosphere. Geneva, Switzerland: IPCC, 1999. 70. US Environmental Protection Agency. Regulatory announcement: new emission standards for new commercial aircraft engines. EPA420F-05-015, available at http://www.epa.gov/oms/regs/nonroad/ aviation/420f05015.htm, 2007. 71. Federal Aviation Administration. Aviation and emissions—a primer, 2005. Available at http://www.faa.gov/regulations policies/policy guidance/envir policy/media/AEPRIMER.pdf, accessed February 2007. 72. Stolarski RS, Krueger AJ, Schoeberl MR, et al. Nimbus 7 satellite measurements of the springtime antarctic ozone decrease. Nature 1986;322:808–811. 73. Air Transport Association of America. ATA Issue Brief: US Airlines support development of alternative fuels. http://www.airlines.org/ government/issuebriefs/Alt+Fuels.htm, October 2006.

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74. Clark C, Martin R, van Kempen E, et al. Exposure-effect relations between aircraft and road traffic noise exposure at school and reading comprehension. Am J Epidemiol 2006;163:27–37. 75. O’Brien K, Friedberg W, Sauer, HH, et al. Atmospheric cosmic rays and solar energetic particles at aircraft altitudes. Environ Int 1996;22(Suppl 1):S9–S44. 76. Boice JD, Blettner M, Auvinen A. Epidemiologic studies of pilots and aircrew. Health Phys 2000;79(5):576–584. 77. Rafnsson V, Hrafnkelsson J, Hrafnkelsson J. Incidence of cancer among commercial airline pilots. Occup Environ Med 2000;57:175–179. 78. Rafnsson V, Hrafnkelsson J, Tulinius H, et al. Risk factors for cutaneous malignant melanoma among aircrews and a random sample of the population. Occup Environ Med 2003;60:815–820. 79. Linnersj¨o A, Hammar N, Dammstrom BG, et al. Cancer incidence in airline cabin crew: experience from Sweden. Occup Environ Med 2003;60:810–814. 80. Gundestrup M, Storm JJ. Radiation-induced acute myeloid leukemia and other cancers in commercial jet cockpit crew: a population-based cohort study. Lancet 1999;354:2029–2031. 81. Zeeb H, Blettner M, Langner I, et al. Mortality from cancer and other causes among airline cabin attendants in Europe: a collaborative cohort study in eight countries. Am J Epidemiol 2003;158(1):35–46. 82. Tokumaru O, Haruki K, Bascal K, et al. Incidence of cancer among female flight attendants: a meta-analysis. J Travel Med 2006;13(3):127–132. 83. Stewart T, Stewart N. Breast cancer in female flight attendants. Lancet 1995;346:1379. 84. Health Physics Society. Report on screening with backscatter x-ray machines. Home page http://hps.org, http://hps.org/ hpspublications/articles/screenindx-ray.html, accessed March 2007. 85. Miniss P, Young DF, Garber DP, et al. Transformation of contrails into cirrus during SUCCESS. Geophys Res Lett SUCCESS Special Issue, October 1997;25(8):1157–1160. 86. Travis DJ, Carleton AM, Lauritsen RG. Contrails reduce daily temperature range. Nature 2002;418:601. 87. Federal Aviation Administration. Order 7110.65R, Air traffic control, Chapter 9, section 4. Fuel Dumping, February 16, 2006. 88. Federal Aviation Administration. Aeronautical information manual. Chapter 6, section 6-3-5. Fuel Dumping, August 3rd, 2006. 89. Good RE, Clewell HJ. Drop formation and evaporation of JP-4 fuel jettisoned from aircraft. J Aircr 17(7):450–456. 90. Clewell H. Evaporation and groundfall of JP-4 jet fuel jettisoned by USAF aircraft. Final Technical Report ESL-TR-80-56. Engineering and Services Laboratory, Air Force Engineering and Services Center, 1980.

RECOMMENDED READINGS American College of Occupational and Environmental Medicine. Occupational medicine practice guidelines, 2nd ed. ACOEM, 2004. American Medical Association. Guides to the evaluation of permanent impairment, 5th ed. AMA, 2001.

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Aerospace Medical Association. Medical guidelines task force, medical guidelines for airline travel, 2nd ed. 2003. Aviat Space Environ Med 2003;74(5): Section II, A1– A6. Aerospace Medical Association. Emerging infectious diseases including severe acute respiratory syndrome: guidelines for commercial air travel and air medical transport. Aviat Space Environ Med 2004; 75:85–86. Friedberg W, Copeland K, Duke FE, et al. Radiation exposure of aircrews. Occup Med 2002;17(2):293–309. Green, KB, ed. The Aviation Industry. State of the art review. Occup Med 2002;17. Levy B, ed. Occupational and environmental health, 5th ed. 2006. Penner JE, Lister DH, Griggs DJ, et al. Intergovernmental panel on climate change special report: aviation and the global atmosphere. 1999. Ribak, J, ed. Occupational health in aviation. Academic Press, 1995. Rom, W, ed. Environmental and occupational medicine, 4th ed. 2007. Rosenstock L, Cullen MR, Brodkin CA, eds. Clinical occupational and environmental medicine, 2nd ed, Elsevier Saunders, 2005. Sohail MR, Fisher PR. Health risks to air travelers. Infect Dis Clin North Am 2005;19:67–84. Thibeault, C. Airliner cabin air quality. Occup Med 2002;17(2):279–292. American Conference of Governmental Industrial Hygienists. Threshold limit values for chemical substances and physical agents.

SUGGESTED WEB SITES Agency for Toxic Substances and Disease Registry (ATSDR). www.atsdr.cdc.gov. American Association of Occupational Health Nurses. www.aaohn.org. American Board of Preventive Medicine. www.abprevmed.org. American College of Occupational and Environmental Medicine. http://www.acome.org. American College of Occupational Safety and Health. www.ACOSH.org. American Conference of Governmental Industrial Hygienist. www .acgih.org. Centers for Disease Control and Prevention. http://www.cdc.gov/travel/. Department of Labor. www.dol.gov. Department of Transportation. www.dot.gov. Environmental Protection Agency. www.epa.gov. Federal Aviation Administration, http://jag.cami.jccbi.gov./cariprofile. asp. Health Physics Society. http://hps.org. International Civil Aviation Organization. www.icao.int/. Intergovernmental Panel on Climate Change. http://www.ipcc.ch/. National Council on Radiation Protection and Measurements (NCRP). http://www.ncrponline.org/. National Institute for Occupational Health and Safety. www.cdc/niosh/ homepage/. Occupational Safety and Health Administration. www.osha.gov. Total Ozone Mapping Spectrometer. http://jwocky.gsfc.nasa.gov/. World Health Organization’s International Health Regulations. http://www.who.int/csr/ihr/ihr1969.pdf. World Health Organization’s IHR 2005. Revision. http://www.who.int/ csr/ihr/IHRWHA583 en.pdf.

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Women’s Health Issues in Aerospace Medicine Monica B. Gorbandt and Richard A. Knittig

My ambition is to have this wonderful gift produce practical results for the future of commercial flying and for the women who may want to fly tomorrow’s planes. —Amelia Earhart

This chapter is primarily concerned with the current state of women’s health as related to aerospace medicine. Although much has been conjectured and written about the training and working of women in the aerospace environment, this chapter addresses the evidence provided in the current state of the literature. Women have made and are making significant contributions across the aerospace spectrum from commercial to military to space flight. As women meet these challenges, the flight surgeon must be aware of issues unique and pertinent to women’s overall health and wellbeing. Except for possibly the latter stages of pregnancy, women have no restrictions or significant limitations in flight performance. The health care professional can be confident about addressing particular women’s health issues as noted in this chapter in standard manner resulting in sustained high performance by women in all aspects of flight or for women participating only as passengers. Women’s involvement in aviation begins with its earliest days that continues currently both in air and space travel. Currently in the United States, women comprise 6% of all Federal Aviation Administration (FAA) pilots with number totaling 36,584 (1). Within the United States military, women make up roughly 6% of all fixed and rotary wing pilots (1). Thirty-two percent of National Aeronautics and Space Administration (NASA) employees are women with approximately 18% serving in scientific or engineering roles. Of the 91 current active astronauts, 18% or 20% are women and of the 15 international astronauts, 2 are women (2). Reviewing FAA data, the number of women in all classes decreased over the last 25 years but this is offset by the remarkable 13-fold increase in the first (air transport pilot) and second class (commercial) female pilot population. 480

Women are represented in all aviation support roles from mechanic to flight engineer, but only constitute a majority in the flight attendant category at 80% (1). Contributions or firsts for women occurred in every decade since the start of powered flight in 1903 by the Wright brothers and continues through today. The following is a brief overview of the few notable contributions and achievements by women in the aerospace field. 1910—Raymond De Laroche of France is the first woman in the world to receive a pilot license. 1911—Harriet Quimby is the first American woman to earn a pilot certification and fly across the English Channel. 1921—Bessie Coleman is the first African American, man or woman, to receive a pilot license. 1932—Amelia Earhart of the United States is the first woman to cross the Atlantic Ocean solo in an aircraft. 1934—Helen Richey, an American, is the first woman hired as a pilot for a United States Commercial Airline. 1942—Mary Van Segue of the United States is certified as the first female Air Traffic Controller. 1942—The United States Women’s Air Force Service Pilots (WASPs) led by Jackie Cochran are the first American women to pilot U.S. military aircraft. 1953—Jacqueline Cochran is the first woman to break the sound barrier done in a Boeing North American F86 Sabre jet. 1963—Valentina Tereshkova of the United Soviet Socialist Republic is a cosmonaut and the first woman in space aboard the Vostok 6. 1973—Emily Warne, an American, is hired as the first female air transport pilot for a modern, jet-equipped scheduled airline, Frontier Airlines.

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PREGNANCY IN AVIATION Policy

FIGURE 22-1 Portrait of Sally Ride, first American woman in space as part of the STS 7 shuttle mission. Courtesy of NASA.

1974—Barbara Raines becomes the first woman pilot for the U.S. military. 1983—Sally Ride is the first American woman in space as part of the STS 7 shuttle mission (Figure 22-1). 1986—Jenna Yeager copilots the Voyager credited with the first around the world, nonstop, nonrefueled flight. 1993—U.S. Department of Defense, through Secretary of Defense, Les Aspin, opens combat aviation to women. 1999—Lt. Col. Eileen Collins of the United States Air Force (USAF) is the first woman to serve as a space shuttle commander. She previously piloted two Space Transportation System (STS) missions (Figure 22-2). 2007—Astronaut Sunita Williams aboard the International Space Station set a record for the number of space walks and total time in space walks for a woman at four walks totaling 29 hours 17 minutes.

FIGURE 22-2 Lt. Col. Eileen Collins of the United States Air Force, the first woman to serve as a space shuttle commander. Courtesy of NASA.

Standardized policies regarding routine national and international commercial travel of pregnant passengers are nonexistent (3). Civil air company policies, however, do take into account the length of the pregnancy. The more advanced the gestation, the more likely rupture of membranes, labor, or delivery will occur. Predictors for many pregnancy-related events are not always readily evident. Fifty percent of the pregnancies that result in preterm delivery have no identifiable risk factors (4). What are the implications? Diversion for even a commuter flight can be expected to take 30 to 45 minutes depending on meteorologic conditions and air traffic. Responding commercial airlines in a survey by Breahtnach et al. reported that only 70% trained aircrew in delivery and fewer than 30% had a full delivery kit (3). Therefore, a conservative approach with some flexibility is generally employed. Many airline medical departments allow pregnant travelers to fly at their discretion to 36 weeks estimated gestational age for domestic flights and 35 weeks for international, or specifically, transcontinental or transoceanic flights (5). Exceeding airline restrictions generally requires a medical provider statement verifying that labor is not imminent and no underlying complications exist. Women with complicated pregnancies may encounter other risks with air travel. Absolute contraindications to air travel include ruptured membranes, bleeding during pregnancy, diagnosed ectopic pregnancy, and severe preeclampsia. First trimester bleeding can represent an undiagnosed ectopic pregnancy or threatened/incomplete abortion. Fifteen to 20% of clinically recognized pregnancies end in spontaneous abortion. Second and third trimester bleeding can represent labor, incompetent cervix, abruption, or placenta previa (6). Pregnancies complicated by multiple gestations, a history of preterm labor (PTL), or existing uterine irritability are predisposed to early delivery. Severe anemia affects oxygen delivery to the placenta and should be corrected before flight or minimally necessitates in-flight oxygen supplementation. Oxygen therapy should also be supplied for conditions that potentially compromise placental reserve such as intrauterine growth restriction, postmaturity, and preeclampsia. The risk with air travel in pregnancy may be minimal in comparison to the environmental risk, such as endemic malaria, that may be encountered in the ultimate destination. The best policy is to consider all aspects of the proposed journey including lodging, activities, food, and medical support, and to mitigate risk that each of these elements poses by establishing sound prenatal care. Pretravel prenatal care typically includes ultrasonography, assessment of immune status to various infections, the need for immunization, malaria prophylaxis, and creation of a prenatal record. Ultrasonography facilitates more precise dating of the pregnancy and helps confirm suspected multifetal gestation and ectopic pregnancy. Non contraindicated immunizations can be administered. Typically, live viral vaccinations such

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as mumps, rubella, oral polio, varicella, and yellow fever are avoided in pregnancy. Prescriptive medications, including malaria chemoprophylaxis and other stand-by therapies such as antiemetics and antidiarrheals should be considered (7). The prenatal record should be carried together with the passport, visa, and immunization records. Pregnant aircrew have distinct responsibilities and required activities in the performance of their flight duties. The changing balance, flexibility, mobility, and body habitus in pregnancy become evident in the second trimester and may interfere with the ability to safely pilot or assist passengers during an emergent egress. Therefore, commercial aircrew is generally restricted from duties after 28 weeks or completion of the second trimester (8). Although pregnancy is not disqualifying in general aviation, the aircrew must be made aware of the impact flying has on the third trimester such as cockpit ergonomics and placental reserve. Placental maturation continues throughout pregnancy. Maturation beyond 34 to 36 weeks is affiliated with several processes including microcalcification deposition that affect oxygen delivery to the fetus and ultimately lower fetal respiratory reserve. This lowered reserve may not pose a problem in the uncomplicated pregnancy in an oxygen tension encountered at 8,000 ft (the commercial cabin), but may become problematic for the nonacclimated fetus in an oxygen tension encountered at 14,000 ft (general aviation, nonpressurized cabin). Women who fly high-performance military aircraft or are engaged in aerial aerobatics will experience high levels of accelerative force (G force). Egress through an ejection seat will result in higher accelerative force. These forces can be sudden, unexpected, and violent and may pose an unacceptable maternal or fetal risk in the gravid aviator. Resultant outcomes would be dependent on gestational age. Significant first trimester insults are likely limited to a fetal loss with no immediate bleeding and would not result in any additional maternal morbidity beyond the nongravid female. Therefore, the gravid female aviator would be just as successful piloting the aircraft or surviving the egress. Significant second or third trimester exposure poses the additional risk of uterine rupture. Twenty percent of cardiac output flows to the uterus by 30 weeks. Therefore, rupture of the uterus or placental abruption would likely result in both fetal loss and profound maternal morbidity or mortality. In this scenario, it is unlikely that she would be able to pilot the aircraft (aircraft loss) or survive the ejection. There are no available studies that address these issues, and pregnant aviators should seek counsel from both their obstetrician and their flight surgeon to determine the point in the pregnancy where temporary grounding would be appropriate. Informed consent must be universally applied to performance aircraft or platforms with ejection seats.

system-specific maternal physiologic changes of pregnancy as well as fetal physiology in order to perform appropriate consultation and policy promulgation for the gravid female or provide aeromedical evacuation (AE) en route care for the pregnant (or newly postpartum) patient. As an example, an asymptomatic 31-year-old passenger at 30 weeks gestation with focal findings of a systolic ejection murmur with an S3 gallop and lower dependent edema is likely normal and cleared to schedule her commuter flight as opposed to same findings and suspicion of heart failure in a nongravid female of the same age.

Physiology Impacts in Flight

Maternal The air travel impacts on the gastrointestinal physiologic changes of pregnancy are occasionally manifested by abdominal pain and nausea/vomiting. Intestinal gas expansion, occurring at altitude, can cause bloating and

The unique physiology of pregnancy is impacted by the flight environment (Table 22-1). In general, these considerations apply to the gravid aircrew/frequent flyer or the infrequent traveler. Aeromedical providers must have familiarity with

Fetal Monitoring of maternal and fetal physiologic reactions during commercial flights demonstrate moderate, but significant maternal cardiopulmonary changes, including a transcutaneous PO2 drop of 25% at maximum cabin altitude (7,855 ft), but no concomitant fetal tachycardia, bradycardia, or loss of variability (9). Therefore, this cabin altitude, corresponding to a maternal PaO2 of 64 mm Hg and an oxygen saturation of 90%, introduces a maternal hypoxia that does not appear to acutely affect the normal fetus. For periods up to 30 minutes, animal models have demonstrated that during a sudden decompression at 15,000 ft, maternal arterial PO2 drops to 46 mm Hg (O2 saturation 82%) without any suspected fetal hypoxic degeneration of the brain or heart. This relative fetal tolerance to hypoxia exists because the fetal oxygen supply to critical organs is maintained through a combination of physiologic advantages of the fetal circulation and fetal compensatory mechanisms such as redistribution of blood flow to vital organs (shunting) and decreased oxygen consumption (10). There are three physiologic advantages of the fetal circulation in matters of oxygen-carrying capacity and dissociation. First, the fetal circulation carries more hemoglobin (gm/dL) than the adult. Second, the fetal hemoglobin (HbF) oxygen dissociation curve is shifted to the left of adult hemoglobin (HbA), and thereby allows 20% to 30% increased oxygencarrying capacity in the fetus. Lastly, the Bohr effect has a positive influence on gaseous oxygen transfer on the hemochorial circulation. Fetal blood, derived from the umbilical blood flow, enters the fetal placenta carrying large amounts of carbon dioxide that rapidly diffuses into the intervillous spaces of the maternal placenta. Local loss of carbon dioxide makes the fetal blood more alkaline and shifts the oxygen dissociation curve left and upward. The opposite occurs with maternal carbon dioxide gain. As a result, the oxygenbinding capacity of fetal blood is raised while maternal blood is lowered, thereby allowing for enhanced oxygen transfer. The Bohr effect operates in one direction for maternal blood and in the other for fetal blood (11).

CHAPTER 22

TABLE a The

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22-1

Potential Maternal Aeromedical Impacts of the Flight Environment on the Gravid Female

Organ System

Physiologic Change of Pregnancy

Cardiovascular

Decreased systemic vascular resistance and increased venous capacitance Increased tidal volume, decreased total lung capacity, and decreased residual volume yielding physiologic dyspnea of pregnancy Increased plasma volume yielding nasopharyngeal edema (compounded by nasopharyngeal hyperplasia) Increased clotting factors and fibrinogen, uterine compression of the vena cava (venous stasis) Delayed gastric emptying, nausea vomiting of pregnancy Slowed GI motility, mild distension Altered lumbar curvature, gravid uterine impingement, joint laxity

Respiratory

Hematologic

Gastrointestinal

Musculoskeletal

Changing center of gravity a

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Flight Environmental Threat

Potential Maternal Aeromedical Impact (s)

Prolonged immobility

Vasovagal response, syncope

Decreased cabin PAO2

Worsening dyspnea

Ambient pressure changes

Barosinusitis, baro-otitis, syncope

Prolonged immobility

Thromboembolic phenomenon

Motion (air sickness)

Nausea/vomiting

Ambient pressure changes Prolonged immobility, aircraft vibration, poor cockpit ergonomics Turbulence

Abdominal distension, colic Low back pain, pelvic pain

Altered balance and increasing risk of traumatic fall

See also Chapter 8.

colicky abdominal discomfort or pain that is compounded by abdominal crowding from the pregnancy. Therefore, gasproducing foods should be avoided a few days before the flight. Nausea of early pregnancy may be compounded by air travel. Therefore, physicians should consider prescribing antiemetics for these women (8). The enlarging, gravid uterus alters the center of gravity and lends to a more unsteady gait. Loss of balance and lack of coordination increases the risk of falls. Ligamentous laxity and vascular engorgement increase the risk of injury. Thirdtrimester abdominal trauma may cause a placental abruption. Because air turbulence cannot always be predicted, the seat belt should be worn at all times when seated. The belt should be fastened low near the pubic symphysis or on the upper thighs in order to reduce the potential injury to abdominal contents. Cabin ambulation in the third trimester should be done with caution (8). Most data confer a weak association between air travel and venous thromboembolic phenomenon (12). Pregnancyaltered clotting factors, thrombophlebitis, and dependent venous stasis, attributed to volume expansion and obstruction of the vena cava from uterine compression, increase the risk of thromboembolic phenomenon in flight. These pregnancy-related changes begin late first trimester and persist to 6 weeks postpartum. This risk may be potentiated by being immobile in cramped seats for long periods of time. Loose-fitting clothing should accompany periodic leg

stretching and hourly ambulation (when possible) in flight. Gravid women with a prior thromboembolic event or additional factors that predispose them to venous thrombosis should consult their physician regarding anticoagulation with low molecular weight heparin. The efficacy of acetylsalicylic acid in preventing deep vein thrombosis (DVT) is conflicting (5). Support stockings, frequent movement, loose clothing, and adequate hydration may diminish DVT risk (6).

Aeromedical Evacuation of the Obstetric Patient Perinatal regionalization, emphasized strongly beginning in the 1990s, has been associated with improved outcome for very low birth weight infants and for women with complications requiring intensive services. This phenomenon involves stabilization of the mother, intrauterine transfer, and the optimum delivery at a medical center that has the volume to sustain costly technology and specialized personnel (13). Generally, the best and most efficient fetal transport mechanism, delivering oxygen and nutrition to the fetus, remains the gravid mother. Clinical circumstances may dictate it is safer to transport medical personnel to the patient than transport an unstable patient in an unstable environment. General contraindications to maternal air transport include maternal instability, a rapidly deteriorating fetus, imminent delivery, lack of experienced (en route) medical

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attendants, and hazardous flight conditions (meteorologic). This assessment of transport versus local care is best left to the accepting or aeromedically validating perinatal team. As with all medical evacuation, arrangements for transfer should be made before the transport. Standing agreements with referral hospitals should be established to provide sufficient guidance for transport and provide communication consistency (14). The transport team should be familiar with the aviation environment and skilled in perinatal care that includes the ability to perform a vaginal delivery. When possible, the evacuating platform should be suited to support equipment that may be needed during transport. Standard equipment includes a delivery kit, uterotonics, oxygen, intravenous fluids, an infant warmer, and maternal and fetal stabilization equipment. Pharmacologic agents such as tocolytics, oxytocin, calcium gluconate (magnesium toxicity), antihypertensives, and antiemetics are useful while handling the more common complications during transport (Table 22-2). Preflight assessment and preparation typically include a cervical check [except in suspected placenta previa or preterm premature rupture of membranes (PPROM) without labor] and intravenous access and adequate airway, if indicated. Transport in a left lateral recumbent position displaces the gravid uterus off the vena cava and thereby increases maternal venous return and subsequent cardiac output and uterine perfusion. Advanced cardiac life support considerations are the same as for the nongravid female. The fetal heart rate can be assessed with a handheld Doppler with digital display (14). Oxygen supplementation should be used liberally as it improves fetal cerebral cortical oxygen tension (15). Planning the AE, including the decision to use fixed wing or rotary aircraft, depends on a myriad of factors including available assets, meteorologic conditions, geography/terrain, airfield support, landing areas, and the distance to the nearest appropriate medical facility (14).

TABLE

22-2

Diagnosis and In-flight Complications of Aeromedevac Transport of Obstetric Patients Diagnosis (in %) Preterm labor (PTL) Preterm premature rupture of membranes (PPROM) Pregnancy-induced hypertension PTL and PPROM Other

Complications (in %) 33.0 21.3

Nausea/vomiting Increased contractions

21.3

Othera

15.0 7.0

3.0

7.5 8.8

a Other included hypertension, hypotension, and decreased maternal respiratory drive. (From O’Brien DJ, Hooker EA, Hignite J, et al. Long-distance fixed wing transport of obstetrical patients. South Med J 2004;9:816–818.)

Most AE transports will occur for fetal purposes and fall in three categories or a combination of PTL, PPROM, and pregnancy-induced hypertension(PIH)/preeclampsia (Table 22-2). In patients who present with PTL or PPROM, tocolytic therapy is frequently employed before or during air transport. The goal of this therapy is to prevent in-flight delivery and allow time for administration of corticosteroids (promote fetal lung maturity) and group B streptococcus prophylaxis (prevent meningitis and other potential infections). These three measures have been shown to reduce perinatal morbidity and mortality attributed to prematurity (4). Severe maternal hypertension or PIH can be complicated by pulmonary edema, eclampsia, and fetal compromise. En route care for eclampsia includes blood pressure control, maternal seizure control and suppression, injury prevention, oxygenation, and minimizing the risk of aspiration. Use of magnesium for seizure control must be closely monitored because it can diminish the maternal respiratory drive in high doses and cause apnea (14).

Outcomes The preponderance of existing evidence, albeit limited, indicates that the commercial aircraft is not deleterious to pregnancy. This sentiment is shared by 93% of obstetricians in the United Kingdom (16). As discussed, the oxygen levels at normal operating altitudes in pressurized aircraft are adequate for the normal fetus in flight. Pregnancy outcomes for chronic exposure to altitude by way of the aircraft do not significantly deviate from the norm (17,18). Similarly, data examining spontaneous pregnancy loss in flight attendants indicates that there is no difference in miscarriage rate from the general population (19,20).

COSMIC RADIATION AND IMPACT ON PREGNANCY AND FEMALE HEALTH Except for the occasional solar particle event, cosmic radiation exposures for the infrequent traveler are minimal and are unlikely to influence pregnancy outcomes such as spontaneous abortion, growth restriction, congenital malformations, mental retardation, and childhood malignancy induction (21). However, exposure for the frequent gravid traveler or aircrew must be weighed, and in certain cases, controlled. Cumulative fetal exposure less than 20 mSv should not result in harm (22). It is prudent to apply a buffer to this value. Therefore, organizations and/or medical providers should communicate risk and implement administrative controls such as modifying work schedules or choosing alternative means of transportation in order to ensure that the cumulative conceptus dose does not exceed 1 mSv (International Commission on Radiological Protection) (23). Depending on the controlling regulatory body, risk communication and control implementation may be either advisable or regulatory in nature (21) (see also Chapter 8).

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Several studies have looked for an excess of radiationinduced cancer, specifically melanoma and breast, in female aircrew. A recent meta-analysis has indicated a slight, significant excess of breast cancer incidence reflected in the cumulative relative risk (RRc) of 1.41 (1.22–1.62) (p 15 min, disconnect autovent supply hose from regulator at quick disconnect (QD).

•

•

Attach patient valve to ET tube. Secure O2 line as needed.

• •

•

Use an alcohol pad to clean used equipment. Restow RSP.

•

Vallecula

Arytenoid cartilage

Epiglottis

Tongue

11. Advance cuffed end of ET tube along right side of mouth, past vocal chords and into trachea until entire cuff is about 1.3 cm or (0.5 in.) below vocal cords. 12. Inflate ET tube cuff with air from 10 mL syringe, remove stylet, and hold ET tube firmly in place. 13. Attach ambu bag to ET tube and give the patient two breaths. 14. Check for breath sounds in both lungs, and if necessary, reposition ET tube until breath sounds confirmed. 15. If intubation and ET tube repositioning unsuccessful, remove ET tube, hyperventilate the patient for 30 s and reattempt procedure starting at step 5. 16. If successful, tape ET tube securely in place. 17. Remove ambu bag and attach RSP patient valve to ET tube. 18. Deliver oxygen through RSP ventilator (BPM = 12, TV = 800, Reg = 12 L/min).

Glottic opening

Vocal cord

FIGURE 23-4 Original respiratory support pack cue card. BPM, beats per minute; CHeCS, Crew Health Care System; ALSP, advanced life support pack; ISS, International Space Station.

•

Complete patient treatment per ISS medical C/L or surgeon instructions.

•

Patient NOT transported to earth • If patient is to remain on autovent >15 min, insert HME between patient valve and ET tube.

No

Set Autovent BPM = 12 initially Set Autovent tidal volume = 800 mL √For O2 flow by observing movement in green indicator on top of patient valve and by feeling for O2 flow

•

Note For detailed intubation procedures go to {Cardiopulmonary Resuscitation: CPR - TRACHEAL INTUBATION} (SODF: ISS MED: BASIC LIFE SUPPORT). 1. Unstow: Endotracheal (ET) tube with stylet (Airway-15) Xylocaine jelly (Airway-14) 10 mL syringe (Airway-12) Laryngoscope (Airway-16) Ambu bag (ALSP-6) Stethoscope (ALSP-1) 2. Insert 10 mL Syringe into one-way valve of ET tube and inflate cuff. 3. Remove 10 mL syringe to confirm cuff and valve integrity (cuff stays inflated). 4. Replace 10 mL syringe and deflate cuff. 5. Lubricate cuffed end of ET tube with xylocaine jelly. 6. Hyperventilate the patient for 30 s. 7. Open the patient’s mouth with right hand. 8. Hold laryngoscope in left hand, and insert laryngoscope blade into the patient’s mouth. 9. Advance laryngoscope blade into space between base of tongue and epiglottis. 10. Lift tongue with laryngoscope blade tip to expose the vocal cords.

ALSP (red)

•

Intubated O2 to ET tube • For use only in intubated patient • Set regulator flow rate = 0 L/min (CAUTION: use WHITE Indicator line).

Will patient be transported back to earth through shuttle?

Remove ambu bag from ALSP and attach ambu bag O2 supply hose to regulator hosebarb.

•

Patient transported to earth • Remove patient extension hose from RSP lid pocket and remove one heat and moisture exchanger (HME) from RSP. • Attach top (small end) of HME to L-shaped end of extension hose. • Quickly disconnect patient valve from ET tube, connect HME to ET tube, and connect extension hose to patient valve. • Retrieve portable breathing apparatus (PBA). • Obtain ISS manned systems extension O line from node or airlock. 2 • Connect extension O line to space shuttle O source: Panel M069M/M032M. 2 2 • Switch O supply from ISS CHeCS rack to PBA. 2 • Move patient to shuttle. • Switch O supply from portable O bottle to shuttle O source through 2 2 2 extension line. • Secure patient in shuttle for return to earth. • Secure autovent, regulator, patient valve, and all flex lines near patient with velcro straps in RSP lid.

Yes

√Output by feeling for O2 flow from regulator hosebarb with hand

√Output by feeling for O2 flow from regulator hosebarb

• •

Unsconscious O2 to ambu bag • Turn autovent BPM knob = dot • Set regulator flow rate to 12 L/min (CAUTION: use WHITE Indicator line).

RSP Setup 1. Deploy RSP. 2. Remove metal dustcap from regulator supply hose and connect to CHeCS O2 supply hose. (**If CHeCS O2 supply unavailable, attach PBAs or shuttle O2 source). 3. Decide whether to use low flow mask, ambu bag, or intubate. (If intubating, attach patient valve to ET tube. Set RSP, BPM = 12, TV = 800). 4. Determine if additional treatment is required.

Conscious O2 to low flow mask • BPM knob = dot • Set regulator flow rate = 12 L/min (CAUTION: use WHITE indicator line).

PCS Airlock: ECLSS O2 Lo P Sply Vlv AL O2 Lo P Supply Vlv cmd Open Verify actual position OPEN.

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505

Respiratory support pack cue card #1 (Flight information) Unconscious patient 4. Set Regulator 6. Place ambu 8. Set Regulator 11. √ Patient bag on flow rate = 12 flow rate = 0 Valve for patient and (CAUTION: (CAUTION: movement of give one Use WHITE Use WHITE green indicator 2. Pull red metal cap breath every indicator line) Indicator line) on top and feel off of regulator 5 s while for O2 flow Set autovent supply hose and 9. 5. From ALSP, preparing BPM knob = 12 12. Attach Patient connect to O2 retrieve blue ILMA (in Valve to ILMA supply (**if CHeCs ambu bag and IK/A) 10. Set autovent is unavailable, use attach O2 7. From IK/A, Tidal Volume 13. Contact flight PBA) tubing to RSP insert ILMA surgeon = 800 Regulator using ILMA 3. Set autovent BPM hose barb 14. Monitor patient cue card Knob = dot (•)

1. Deploy RSP, ALSP, and defibrilator

Conscious patient 1. Deploy RSP, ALSP and denbrillator 2. Pull red metal cap off of regulator supply hose and connect to O2 supply (** if CHeCs is unavaliable, use PBA) 3. Set autovent BPM knob = dot (•)

4. Set Regulator flow rate = 12 (CAUTION: Use WHITE indicator line)

7. Contact flight surgeon

5. Remove Low flow Non-Rebreather Mask from RSP IId pocket and attach O2 tubing to Regulator hose barb.

8. Monitor patient

6. Put mask on patient

FIGURE 23-5 Revised respiratory support pack cue card onboard the International Space Station. ALSP, advanced life support pack; ILMA, intubating laryngeal mask airway; BPM, beats per minute; IK/A, intubating kit/airway; CHeCS, Crew Health Care System; PBA, portable breathing apparatus.

• Use color where feasible for identification, but do not overuse color (e.g., for decoration) • Highlight important words with the use of bold, underlined, or bordered text

Conclusion Human-system interfaces are very crucial for the overall system performance. If the interfaces are designed properly, the users can do their tasks safely and efficiently, with minimal errors, training, and stress. If an iterative design process is used in the development of user interfaces, the outcome will be effective and efficient. The key to optimum design is to thoroughly identify the user requirements and needs up front, design the user interface for accommodating these requirements, and test and retest the design to verify and validate that the correct requirements are used and are met.

Crew Resource Management Overview CRM is formal training for aircrew designed to improve crew coordination, communication, and ultimately safety in aviation. It has been defined as the effective use of all available resources: human resources, hardware, and information in order to achieve a safe flight (30,31). Typically, modern CRM programs include training in teamwork skills, leadership, decision-making, and communication, as well as primary education in human factors. Originally termed Cockpit Resources Management, the current Crew Resource Management more accurately reflects the inclusion of non–pilot aircrew and other personnel whose actions impact on flight safety. In the United States, the Federal Aviation Administration (FAA) requires CRM training for all commercial carriers; guidelines for training as well as its design and implementation are currently described in FAA

Advisory Circular 120-51E (32). CRM has become a globally recognized practice to improve aviation safety. Outside the United States, similar requirements and guidelines are provided by other flight safety authorities, such as the International Civil Aviation Authority (ICAO) (31) and the Civil Aviation Authority (CAA) in the United Kingdom (33), as well as numerous military commands around the world. Despite a common perception that the objective of CRM is ‘‘better teamwork,’’ the true purpose of these programs is to improve flight safety through appropriate management of human resources. Properly executed training programs go well beyond the basic concept of ‘‘team training,’’ and are integrated with more conventional technical skills training, often using flight simulation as a key mode of delivery. Continual reinforcement of CRM skills is an essential element of ongoing airline or squadron line operations. In recent years, CRM has been extended to include ongoing assessments of threats to safety by aircrew and the management of errors that are, to some extent, inevitable in technologically complex operational environments; a concept recently termed Threat and Error Management. In TEM, crews go beyond the rote application of learned CRM skills and focus on risks and threats that present themselves through the flight. Bad weather, for example, may be identified en route, with discussion of the safety implications that it presents, and a crew-level analysis of the best course of action to minimize the risk presented. TEM also involves the idea that errors and mistakes by crewmembers will occur in any flight, and a nonblame approach to error is emphasized. By shifting the focus from blame to safety, the error is dealt with as any other threat to safety, and best course of action is discussed in an open atmosphere to determine the most appropriate response to the new situation.

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Illustrative Description Origins Formal CRM training in commercial aviation appeared at the end of the 1970s, a decade in which human error and human factors were frequently identified as contributing causal factors in a number of high–profile aviation disasters. Among the most often cited accidents is that of Eastern Airlines Flight 401. Flight 401 was a Lockheed L-1011 passenger jet traveling from New York to Miami on December 29, 1972. Problems arose while the aircraft was on final approach into Miami International Airport when a gear down-and-locked confirmation indicator light failed to illuminate. The crew elected to abort the landing, climbed to holding altitude, and engaged the autopilot. As they tried to identify the source of the problem, the autopilot inadvertently became disengaged and the aircraft lost altitude. The crew remained unaware of the dropping altitude, and the aircraft impacted the everglades swamp at 227 knots. Of the 176 people onboard, 101 died on impact, and 2 more in the days that followed. Investigation by the NTSB concluded that during the final few minutes of flight, the crew failed to monitor the flight instruments and aircraft status during this critical period of low-altitude flight. Examination of the wreckage found that the gear was actually down-and-locked, and the indicator light failure was due to a burned-out bulb (34). Another highly significant accident was the runway collision of a Royal Dutch Airlines (KLM) 747 and a Pan American Airlines (Pan Am) 747 on the island of Tenerife on March 27, 1977. With 583 people killed, this accident remains the single worst accident in aviation history. These aircraft were among several that had been diverted to a secondary airport on Tenerife when a terrorist bomb temporarily closed Gran Canaria International, the main airport for that island. This diversion, combined with long duty hours and bad weather, set the stage for confusion during taxiing and takeoff later that day when Gran Canaria reopened. The collision occurred in the fog as the KLM aircraft attempted takeoff and as the Pan Am jet taxied along the same runway. Seeing the Pan Am aircraft at the last minute, the KLM pilot attempted to climb over the taxiing aircraft but failed to do so, shearing off the top of the Pan Am jet and causing both aircraft to burst into flames. Failure to obtain proper clearance, the cumulative effects of long flight times and delays, command style, confusion over flight and ground control, and nonstandard radio communication have all been identified as contributing factors in this accident. Following these and other accidents, NASA convened a workshop in 1979 to address aviation safety in general, and crew factors specifically (35). Failure in communication, problems of task fixation, loss of situational awareness, and errors in decision making were all identified as recurrent and critical issues in numerous accidents in the preceding years. Data suggested that up to 70% of accidents were due to crew issues, as opposed to mechanical, maintenance, or weather (36). Formal training in crew management was proposed as a solution, and the term cockpit resource management was born.

On the basis of the models borrowed from management consulting, early CRM programs strived for both task-oriented and team-oriented approaches to crew management. In the early 1980s, United Airlines became the first U.S. carrier to create a formal CRM program, combining theoretic foundations with simulator-based training (37). Many of the fundamentals of CRM were established in this early program, including the establishment of expectancies for crewmembers to raise safety concerns whenever present, providing clear guidelines for decision making, and defining rational approaches to conflict resolution. It is important to note that while CRM represented a training solution for all pilots, many pilots would have already exhibited this optimal style of cockpit management, and that such a style would have been described as superior airmanship or excellence in captaincy in the days before formal CRM. In some ways, CRM can be thought of as taking that mix of skills already present in good pilots, and packaging it in a training program so that all aircrew can achieve that same level of safety and crew performance on the flight deck. Current Standards in Crew Resource Management Training CRM training has gone through a number of significant changes since first developed. One important advance has been the shift from a cockpit-centered training model to one that includes cabin crew and other personnel whose actions have the potential to impact upon flight safety. This change has been reflected in the aforementioned shift of CRM from cockpit to crew resource management. Well-trained crews ensure the timely flow of critical information to and from the cockpit and create an environment where safety exists as a super ordinate goal for all crewmembers. The concept of shared mental models has emerged as one of the key elements in maximizing crew coordination (38). Helmreich has described at least six discrete generations of CRM over the last 25 years, each with fundamental advances in both theory and application over its predecessor. Current welldesigned CRM programs focus on continual reassessment of threats to safety. This approach accepts the inevitability of occasional crew errors and stresses the need to trap and manage those errors when they occur. This approach has been termed threat and error management and represents the state of the art in CRM currently (39). As mentioned previously, FAA Advisory Circular 120-51E describes the current FAA requirements for CRM training. This document divides required CRM components into two broad areas, (a) communication process/decision behavior and (b) team building and maintenance. The first topic area includes briefings, assertion, self-critique, conflict resolution, communication, and decision making. The second topic area includes leadership, followership, concern for task, interpersonal skills and group climate, workload management, situation awareness, individual factors, and stress reduction (32). These guidelines also describe key aspects of successful programs, including the need for initial indoctrination training, subsequent recurrent training, and

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reinforcement throughout routine line operations at all levels. While the FAA grants authority for actual course design to individual airlines (in order to customize needs to specific carrier operations), all programs must meet the guidelines as set out in the advisory circular. Two recent reviews by Salas et al. from the University of Central Florida identified considerable variability between carriers in terms of how the requirements laid out in AC 120-51e are operationalized at various airlines (40,41). This raises the question of whether the current approach to implementing CRM is optimal. Efforts to export CRM programs from one airline to another, and from U.S. carriers to non–U.S. carriers, have proved problematic due to differences in organizational culture and specific flight operations. Furthermore, attempts to export specific CRM training programs from U.S. carriers to non–U.S. carriers have met with difficulty. Fundamental elements of CRM, such as encouraging junior officers to voice their concerns to more senior captains involve issues such as challenging authority and countering command hierarchies. Such practices may seem simple and appropriate in typical western and northern European cultures, but are more complex in those countries that typically have steep authority gradients. Conversely, many cultures are typically more rule-adherent than western cultures. Crews from such backgrounds operate with different behavioral ground rules, and SOPs may be expected to be followed more closely than in the West. Helmreich has written extensively on differences in organizational culture and national culture, and how these differences affect CRM training. The lesson appears to be that training programs need to be tailored to the specific environment of each airline, and that the national norms of social structure and communication need to be addressed in curriculum design (41,42). Future Challenges A series of studies conducted in the 1990s suggested significant individual variation in pilots’ responses to CRM training programs. Earlier it was suggested that some pilots might naturally exemplify superior CRM skills, even before exposure to training. The opposite is also likely true; some pilots may not be well suited to the concepts taught in CRM training. Helmreich has identified two subsets of individuals, one subset with high-achievement needs but with high levels of interpersonal hostility, and another subset with overall low-achievement motivation. Both sets of individuals have been identified as potentially problematic when it comes to CRM skills and training receptivity∗ . Pilots with high hostility were found to reject CRM concepts as measured in post–course attitude questionnaires (43), presumably because skills taught were incongruent with their personal ∗ Helmreich describes the subset of individuals with high-achievement needs but also high levels of interpersonal hostility as the Wrong Stuff, and the other subset of individuals with low-task motivation as No Stuff. This somewhat tongue-in-cheek description is in contrast to the concept of the Right Stuff described in Tom Wolfe’s account of the early test pilots and astronauts (41)

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management style. In flight simulation studies, crews with captains from both groups (low motivation and high hostility) performed more poorly than pilots with high motivation and good interpersonal skills (44,45). These studies are often cited as justification for the use of psychological testing in the selection of both pilots and astronauts. They also suggest that while CRM training may be an effective tool to improve flight safety, individual factors cannot be ignored, and the degree to which CRM can compensate for poor natural leadership is not well understood. Another issue of some controversy is the degree to which CRM has actually achieved its goal of improving flight safety. Such research has proved challenging, and definitive proof of effectiveness has remained elusive. Salas et al. have conducted several reviews over the last few years in an attempt to determine the degree of supporting evidence for the effectiveness of CRM. The evidence for positive receptivity among trainees is strong, and there is also good evidence that attitudes following training show positive shifts in desired directions. Studies demonstrating actual behavior change are difficult to conduct, and evidence of this finding is much more difficult to gather. Actual impact on flight safety has proved exceedingly difficult to measure. CRM has been implemented over the last 25 years in concert with a myriad of other safety initiatives, including improved weather radar, wind shear detection systems, improved autopilot and automation, and so on, making it difficult to attribute improvements in safety to any one factor. It is probably safe to say, however, that there is significant face validity to the concept of CRM, and anecdotal reports of its success are relatively commonplace. One of the most commonly cited examples of such evidence was the flight of United Airlines (UAL) Flight 232. This aircraft, a fully laden DC-10, experienced a catastrophic hydraulic failure and loss of one of three engines en route from Denver to Chicago on the afternoon of July 19, 1989. By any account, the resulting complete loss of hydraulics rendered the aircraft unmaneuverable, and expectations were that the aircraft would inevitably crash and all personnel would perish. In what remains an outstanding display of piloting ability and ingenuity, Captain Al Haynes and his crew (including a DC-10 instructor pilot who was deadheading as a passenger) managed to devise a means of controlling the aircraft using differential thrust with the two remaining engines. Despite all expectations, the crew managed to land the aircraft at Sioux City, Iowa, losing control only in the final feet of decent. Although the aircraft cart wheeled down the runway and burst into flames, many passengers and crew survived. Haynes has long attributed his ability to fly the damaged aircraft to skills he acquired in United Airline’s CRM training program, and this crash landing and the survival of more than half the passengers onboard remains one of the great success stories of CRM to date.

Conclusion Few people with firsthand experience in aviation consider CRM training to be either completely ineffective or a

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universal remedy for all matters related to flight safety. There is, however, a general consensus that CRM is an integral component of a comprehensive approach to improving safe flight operations. As aviation technology changes and as computerization and automation play ever increasing and changing roles in aircraft operation, CRM will need to develop to address the challenges and changes in role experienced by aircrew.

Unmanned Aircraft Systems

Traditional aviation Unmanned occupations aviation

Overview This is an exciting time for those directly involved or supporting civil and military aerospace operations given the advent of an entirely new aerospace occupation, the UAS crewmember (see also Chapter 27). For aerospace medicine practitioners, there are both significant challenges and opportunities in addressing the immediate and forecasted future aeromedical needs for this novel and rapidly growing career field. While technology can simplify the operation of a single UAS, it is also increasing the span of control of individual operators, and in the end is creating a diversity of task environments, some of which are more complex than those seen in traditional aviation. The overall trend then is for technology to enhance rather than diminish the role of the human operator in ‘‘unmanned’’ aviation. As such, attending to human performance issues is critical for the success of current and future UAS crewmembers. No different from traditional aircrew, it is the responsibility of aerospace medicine practitioners to function as advocates for UAS crewmembers by using their specialized knowledge to help optimize human performance. Consistent with the fundamental occupational medicine precept of the necessity

of the physician workplace visit, it is important for aerospace medicine practitioners to directly observe and participate in UAS operations because: (i) the diversity of Ground Control Station (GCS) designs prohibits generalizations about UAS task environments based on knowledge gained from an individual UAS, and (ii) current aerospace medicine practice is based largely on a subset of the spectrum of existing and potential UAS task environments (Figure 23-6). Perhaps the sole consistency across the spectrum of UAS is the fact that the crew and the aircraft are no longer necessarily co-located. From an occupational medicine perspective, this makes UAS the engineering control solution for such traditional aerospace medical hazards as hypobarics, hypoxia, acceleration, vibration, thermal stress, and those forms of spatial disorientation associated with acceleration. Nevertheless, UAS historically have suffered mishap rates one to two orders of magnitude greater than those of manned aviation with various studies attributing 17% to 69% of the mishaps to human factors (46). Although aerospace medicine human factors remain pertinent in UAS, there are differences in the relative importance of specific human factors concerns for unmanned versus manned aviation (Table 23-2). Because optimum human performance remains a necessary, albeit not sufficient, condition for the safe and efficient operation of UAS, and appreciating the very heterogeneous nature of UAS task environments, aerospace medicine practitioners should become proficient in utilizing the Human Systems Integration (HSI) model of human performance to consistently and systematically assess the underlying determinants of crewmember performance in individual UAS (Figure 23-7). Past applications of this model have shown that UAS crewmember performance

FIGURE 23-6 An occupational medicine perspective of the diversity of task environments for unmanned aircraft system pilots (external, internal, and multi-aircraft control pilots) relative to traditional manned aviation pilots and air traffic control (ATC) specialists. External pilots control unmanned aircraft through direct visual contact with the aircraft. Internal pilots control unmanned aircraft using information provided through control station displays. Of note, manned aviation and ATC task environments are inclusive of a relatively homogenous subset of UAS task environments. Therefore, caution is required in drawing analogies between manned and unmanned aviation.

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509

23-2

Comparison of Aerospace Medicine Human Factors Concerns for Manned Aircraft (MA) versus Unmanned Aircraft System (UAS) Crewmember Performance Using Human Factors Analysis and Classification System (HFACS) Categories of Preconditions MA

UASa

Technologic environment Seating and restraints Instrumentation Visibility restrictions (e.g., FOV) Controls and switches Automation Personal equipment

+ + + + + + + + + ± + + +

+ + ± 0 ± 0 + 0 + + + + 0

Cognitive Vigilance and attention management Cognitive task oversaturation Confusion Motion sickness Hypoxia and hypobarics Visual adaptation Physical task oversaturation

+ + + + + + + +

+ + + + ± 0 ± +

Perceptual factors Illusion—kinesthetic Illusion—vestibular Illusion—visual Misperception of operational conditions Misinterpreted/misread instrument Spatial disorientation Temporal distortion

+ + + + + + + +

+ 0 0 + + + + +

Crew coordination and communication Distributed/virtual crew Negative transfer Distraction

+ 0 + +

+ ± + +

Factors Physical environment Vision restricted (clouds, ice, etc.) Noise and vibration Windblast Thermal stress Maneuvering forces

MA

UASa

+ +

+ +

Psycho-behavioral Personality style or disorder Emotional state Overconfidence Complacency Motivation Burnout

+ + + + + + +

+ + + + + + +

Adverse physiological states Effects of G forces Prescribed drugs Sudden incapacitation Preexisting illness or injury Physical fatigue Mental fatigue Circadian desynchrony Shift changeovers

+ ± + + + + + + 0

+ 0 + + + + + + ±

Self-imposed stress Physical fitness Alcohol Drugs, supplements, or self-medication Inadequate rest Unreported disqualifying medical condition

+ + + + + +

+ + + + + +

0 0 + + + +

± + 0 ± 0 0

Factors Geographic misorientation (lost) Checklist interference

Miscellaneous Multiaircraft control Control and feedback latency Standardized cockpit design and controls Manual control of aircraft Standardized crew qualifications ‘‘Shared fate’’ with aircraft

+ = usually applicable, ± = possibly applicable, 0 = not applicable. a If a UAS is operated from another airborne platform, all MA performance concerns would also apply. FOV, field of view. Federal Aviation Regulation. Sec. 135.267. http://ecfr.gpoaccess.gov/cgi/t/text/text-idx?c=ecfr;sid=f4637c62296f8bd572410435a95a1bc2;rgn=div8; view=text;node=14%3A2.0.1.4.23.6.11.4;idno=14;cc=ecfr, (accessed 17 July 2007).

is impacted by issues involving the HSI domains of human factors engineering; personnel; training; manpower; environment, safety, and occupational health (ESOH); and habitability (47).

Illustrative Description Domains: Personnel and Training Currently, there are no uniform standards across the U.S. military services for UAS crewmember selection, training, and certification (48), nor are there formal civil standards for the training and certification of UAS pilots (49). Although various organizations are developing

recommendations for standards (American Society for Testing and Materials subcommittee F-38.03; NASA’s Access 5 program (inactive); Radio Technical Commission for Aeronautics (RTCA) incorporated special committee 203; and SAE International’s G-10 Aerospace Behavioral Engineering Technology Committee), there currently exists only a small number of well-designed studies (50–52) addressing the necessary prerequisite knowledge, skills, and abilities for UAS pilots and conflicting findings and expert opinion regarding the value of prior manned aircraft flying experience (49,50,52,53). There are also few studies (51,54) addressing medical certification standards for UAS pilots

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O P E R AT I O N S

UAS crewmember performance Human capabilities/ competencies

Human−Machine Interface Design

Human fitness for duty

Human workload

Crew work distribution

Knowledge, skills, and abilities

Crews qualified, rested, motivated, vigilant, and healthy

Human systems integration Human factors engineering Compatibility of GCSa design with anthropometric and biomedical criteria Workload, situational awareness GCS controls, displays, and automation

Personnel

Crewmember selection and classification

Training pipeline flow

Demographics

Training tasks and training development methods

Cognitive, physical, and educational profiles Accession rates

Media, equipment, and facilities

Attrition rates

Simulation

Effects of GCS design on skill, knowledge, and aptitude requirements

aGCS

Training

Operational tempo

Manpower

Wartime/ peacetime manpower requirement Deployment considerations Force and organizational structure Operating strength Manning concepts

Environment, Safety, and Occ. Health Occupational injuries and illnesses Health hazards induced by systems, environment, or task requirements Human error Total system reliability and fault reduction

Habitability

Physical environment (adequate light, space, ventilation, and sanitation; noise and temperature control) Living conditions

Survivability

Fatigue and stress Potential damage to GCS Protective equipment (NBC)

Personnel services

= ground control station

FIGURE 23-7 Process model for obtaining unmanned aircraft system (UAS) crewmember performance from the domains of human systems integration (HSI) with UAS-relevant examples of HSI elements/areas of concern for each domain.GCS, ground control station, NBC, nuclear, biological, and chemical. (Adapted from Tvaryanas AP. Human systems integration in remotely piloted aircraft operations. Aviat Space Environ Med 2006;77(12):1278–1282.)

based on an empirical analysis of the UAS task environment, and even less data to guide liberalizing current standards in order to address aeromedical accommodation (49). One of the chief barriers in addressing UAS personnel selection, training, and certification issues continues to be the heterogeneity in UAS control station design, and therefore occupational task environments, leading to similar job titles encompassing divergent skill and aptitude requirements based on UAS (Figure 23-8). Some progress has been made in defining a generic, high-level workflow with associated knowledge, skill, and aptitude requirements for USAF medium- and high-altitude endurance UAS (Figure 23-9), but this represents only a fraction of the total UAS spectrum. Domain: Human Factors Engineering The UAS crew is unique compared to traditional aircrew because their task environment is the GCS rather than the cockpit. They often lack peripheral visual, auditory, and somatosensory cueing and are therefore relatively sensory

deprived. They are nearly entirely dependent on focal vision in order to obtain information on vehicle state through either automation and displays or direct visual contact. This effectively limits the crew to the use of the central 30 degree of their visual field and requires them to process information using a neurosensory pathway not naturally adapted to providing primary spatial orientation cues (i.e., focal vision). The effect of this sensory deprivation has not been well researched and little is known where UAS crewmembers direct their attentional focus or what information they use. For instance, a study (55) of visual scan patterns using a MQ-1 Predator head-up display (HUD) revealed nonstandard instrument scan patterns with no adjustment to compensate for the lack of auditory or haptic cueing of engine performance. Additionally, a review of UAS mishaps (46) found that human–machine interface design and crewmember attentional factors were frequent causes of crew-related errors. While offloading perceptual workload to nonvisual channels seems an intuitive solution, preliminary

511

F. Strike

Perform damage assessment

Control laser

Provide sensor support during talk On(s)

Perform weapon launch checklist

Perform weapon prelaunch checklist

C. Aircraft en route

A. Aircraft airborne

Aircraft launch

No UA airborne

Perform mission preparation

Support air space management plan

Complete operations checks

Perform sensor optimization

Tasking complete or Bingo

Divert to other mission

Position sensor system to collect

Perform sensor optimization

Yes UA at base

Yes

D. Reconnaissance

Complete losing handover (MCE)

No

Aircraft secured

Communicate with imagery exploitation teams

Calibrate sensors

A. Pre-mission complete

Set up CGS

E. Aircraft on deck

Complete postflight procedures

Recovery aircraft

Perform sensor optimization

Complete gaining handover (LRE)

B. Changeover

No

Mission trigger

Calibrate sensors

A/C enroute OPAREA

A/C airborne

No

No

Yes

A/C in OPAREA

Off going crew

Complete changeover

Mission complete or bingo

Yes

B. Mid mission complete

Collect EEI

Participate in mission brief

Develop scheme of maneuver

Develop target tracker

Complete target deck

Yes

FIGURE 23-8 Workflow breakdowns for the sensor operator (SO) crewmember in the MQ-1 Predator unmanned aircraft system (UAS) (A) versus the RQ-4 Global Hawk UAS (B). Despite the same job title, the job content is very different based on UAS, making it impracticable to consider these equivalent positions for the purposes of selection and training. UA, unmanned aircraft; CGS, California Geological Survey; OPAREA, operating area; RTB, return to base; MCE, mission control element; LRE, launch and recovery element; EEI, essential element of information.

No

RTB Strike, reconnaissance or RTB

Reconnaissance

Strike

Off going crew

Complete postflight tasks

No UA in OPAREA or base Yes

Navigation to base

Complete changeover

Yes

Perform surveillance en route

Gather target development information

Complete gaining handover checklist

Complete losing handover checklist

Complete sensor calibration

Perform pre-flight checklist

Mission trigger

C. Post mission

Conduct target accounting and statistical reports

SO’s secure

Participate in debrief

Archive data

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O P E R AT I O N S Perform preflight planning No

Yes

Aircraft launch procedures

Only applicable if LRE-to-MCE transition

Conduct aircraft navigation

A/C airborne

Complete changeover

Complete post flight tasks

Complete handover

Contingency planning

A/C at base

Monitor A/C systems

Mission execution phase

Off going crew

No

Yes Only applicable if MCE-to-LRE transition

Complete handover

Recover aircraft

Complete post flight tasks

Aircraft secured

work with multimodal displays has yielded mixed results and still needs to be further studied (56). Advances in automation are decreasing the need for UAS pilots to have traditional pilot skills and instead emphasize monitoring and collaborative decision-making skills. However, the role of passive monitor makes maintaining a constant level of alertness exceedingly difficult and predisposes to ‘‘hazardous states of awareness’’ (57). This was demonstrated in a study (58) of USAF UAS crewmembers that found high levels of subjective boredom and significant decrements in vigilance performance over the course of a single 8-hour shift. Likewise, a study (59) of Army UAS pilots demonstrated degraded target detection and recognition performance as well as longer reaction times during nocturnal operations involving long flights. Although one of the best ways to overcome these effects is work breaks, there is concern for an acute decrement in crew situational awareness when control is transferred to another crew not currently involved in the mission. For example, the aforementioned Army UAS pilots preferred longer over shorter rotations because of the perception that longer rotations allowed for

FIGURE 23-9 Payload independent, core UAS pilot workflow based on synthesis of MQ-1 Predator, MQ-9 Reaper, and RQ-4 Global Hawk task analyses. LRE, launch and recovery element; MCE, mission control element.

better situational awareness of the tactical environment (59). This is consistent with findings from other occupational domains such as ATC (60,61) and even medicine, where patient transfers or handoffs were found to be one of the largest sources of medical errors (60,61). Perhaps most unique of UAS is multi-aircraft control (MAC) where a crew controls more than one aircraft. For example, the recently fielded MQ-1 Predator MAC GCS provides the capability for one pilot and four sensor operators (SOs) to control a maximum of four aircraft. The impact of transforming the role of the UAS pilot from that of a single aircraft operator to a multiple systems manager on knowledge, skill, and aptitude requirements is currently unknown. An FAA-sponsored review of the UAS human factors literature (56) concluded there is only limited research suggesting one person may control more than one unmanned aircraft under relatively idealized conditions to include closely coordinated and correlated activities, a stable environment, and reliable automation. Other research (62) has demonstrated performance controlling even a single unmanned aircraft is significantly degraded when heavy

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demands are imposed by payload operations. This would suggest that the ability of a pilot to attend to multiple aircraft might be severely compromised under nonidealized conditions, especially if an aircraft is malfunctioning or damaged. MAC also introduces new considerations for aerospace medicine practitioners. First, the risk for impaired pilot performance must now be weighed against the potential impact on multiple missions rather than a single mission. Second, MAC allows pilots to delegate limited aircraft control to ‘‘nonpilot’’ crewmembers, thereby causing their duties to encroach on traditional pilot tasks. Finally, there is no data to suggest the necessity or method for adjusting current hours-of-service rules for MAC operations. Domains: Environment Safety and Occupational Health, Survivability, and Manpower The USAF’s strategic vision for UAS suggests ‘‘the absence of onboard aircrew mitigates the historic limitations of aircrew fatigue’’ (63) in UAS operations. However, the introduction of long-endurance UAS has necessitated the implementation of shift work for crewmembers in order to provide the necessary around-the-clock staffing of GCS. Serious public health concerns have been raised regarding the association between the documented effects of shift work and resulting degraded work performance with accompanying increased risk for errors and accidents. These concerns were validated by a recent study (64), which found higher reported fatigue levels among USAF UAS crewmembers as compared to traditional aircrew. Despite the potential for fatigue to be highly prevalent in UAS operations, only limited research has been conducted on the effects of fatigue on UAS crewmember error or its impact on operational efficiency. A simulation modeling study (65) analyzing the effects of fatigue, crew size, and rotation schedule on Army UAS crew workload and performance predicted almost three times as many mishaps would occur when a crew was fatigued as compared to rested. Although the results of the former study have not been operationally validated, an observational field study (58) of USAF UAS crewmembers involved in rotational shift work noted decrements in mood, cognitive and piloting performance, and alertness associated with the acute fatigue of a single shift. This same study also found no association between hours-of-service rules for flying and reported acute or chronic fatigue. Walters et al. notes operational requirements for UAS crewmembers ‘‘may include extended duty days, reduced crew size, and varying shift schedules,’’ which are ‘‘likely to reduce operator effectiveness because of fatigue’’ (65). Restated from an HSI perspective, UAS crewmember performance is at risk because of multiple, potentially synergistic domain shortfalls involving manpower (e.g., extended duty days and reduced crew size), survivability (e.g., fatigue), and ESOH (e.g., reduced operator effectiveness). Additionally, the human factors engineering domain can be added to this mix when the design of the human–machine interface drives human error or inefficiency. Taken together, aerospace medicine practitioners should anticipate baseline-degraded performance in UAS crewmembers, which is an important

513

consideration when recommending performance interventions or consulting on mishap investigations. Additionally, aerospace medicine practitioners should recognize that UAS crewmember work environments are potentially stressful, thereby increasing the likelihood for exacerbations of underlying clinical or psychological conditions. In particular, the adverse chronobiological effects of sustained rotational shift work are an important consideration when making aeromedical accommodation decisions.

Conclusion This section introduced aerospace medicine practitioners to some of the HSI domain highlights underlying UAS crewmember performance. Although it is not reasonable to expect aerospace medicine practitioners to be experts in all these issues, they need to have a working knowledge of the main issues in order to fully understand the task environment and human performance challenges. This is of immediate relevance because current military aerospace medicine practitioners can be expected to make aeromedical dispositions on UAS crewmembers, participate in UAS-focused aeromedical education and training programs, advise UAS squadron leadership on crew performance issues, and provide human factors consultation as members of UAS mishap investigation teams. Additionally, it is not unreasonable to expect that civil aeromedical examiners will be seeing UAS crewmembers in their clinical practices in the near future.

SUMMARY In summary, as stated by Chapanis (66), human factors engineering is the application of human factors to the design of systems, machines, tools, tasks, and environments for safe effective and comfortable human use. Ultimate objectives of human factors include the following: • Facilitating operational efficiency (increase safety, minimize error) • Achieving reliability, maintainability, and availability • Providing user-centered design (improve work environment, reduce stress and fatigue, increase ease of use, comfort, user acceptance) • Other considerations such as reducing loss of time and equipment The key components of the human factors are human capabilities such as cognitive human performance and error, fatigue, anthropometry and biomechanics; humansystem interfaces such as information transfer (displays and controls), human–computer interactions, communications and tools, and environmental factors such as habitability/architecture, noise/vibration, illumination/color, and temperature/humidity. A multiple disciplinary team is needed in order to apply human factors with a systems approach. This team could comprise experts in disciplines such as psychology, industrial engineering, occupational and environmental medicine, applied physiology, anthropometry,

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industrial design, operations research, and statistics. This chapter provided a limited overview of selected human factors components with emphasis on aerospace medicine applications. Readers interested in a more in-depth study of human factors can refer to texts such as: Design Applications Norman’s The Design of Everyday Things (67) Human Factors Sander’s and McCormick’s Human Factors in Engineering and Design (28) Nielson’s Usability Engineering (29) Ergonomics Konz’s Work Design: Industrial Ergonomics (68) Psychology Wicken’s Engineering Psychology and Human Performance (69)

ACKNOWLEDGMENTS Fatigue section supported by National Space Biomedical Research Institute through NASA NCC 9–58; AFOSR F4962095-1-0388 and F-49620-00-1-0266; and NIH NR004281 and NIH RR00040.

REFERENCES Introduction 1. Beaty D. Naked pilot: the human factor in aircraft accidents, 2nd ed. Ramsbury: The Crowood Press, 1995. 2. Human Factors and Ergonomic Society. About HFES. www.hfes .org/web/AboutHFES/about.html, (accessed 11 July 2007). 3. Kohn L, Corrigan J, Donaldson M, eds. To err is human: building a safer health system. Washington, DC: National Academy Press, 1999. 4. Food and Drug Administration. Why is human factors engineering important for medical devices? www.fda.gov/cdrh/humanfactors/ important.html, (accessed 16 April 2004). 5. Stone R, McCloy R. Ergonomics in medicine and surgery. Biomed J 2004;328:1115–1118. 6. Food and Drug Administration. FDA issues bar code regulation. www.fda. gov/oc/initiatives/barcode-sadr/fs-barcode.html, (accessed 12 July 2007).

Fatigue 7. Durmer JS, Dinges DF. Neurocognitive consequences of sleep deprivation. Semin Neurol 2005;25:117–129. 8. Mallis MM, Banks S, Dinges DF. Sleep and circadian control of neurobehavioral function. In: Parasuraman R, Rizzo M, eds. Neuroergonomics: the brain at work. Oxford: Oxford University Press, 2007:207–220. 9. Van Dongen HPA, Maislin G, Mullington JM, et al. The cumulative cost of additional wakefulness: dose-response effects on neurobehavioral functions and sleep physiology from chronic sleep restriction and total sleep deprivation. Sleep 2003;20:117–126. 10. Federal aviation regulation. Sec. 135.267. http://ecfr.gpoaccess .gov/cgi/t/text/text-idx?c=ecfr;sid= f4637c62296f8bd572410435a95a1bc2;rgn=div8;view=text;node= 14%3A2.0.1.4.23.6.11.4;idno=14;cc=ecfr, (accessed 17 July 2007). 11. Federal aviation regulation. Sec. 135.265. www.airweb.faa.gov/ Regulatory and Guidance Library%5CrgFAR.nsf/0/

7416414817B0167C8625694A00702606?OpenDocument, (accessed 11 July 2007). 12. Cruz C, Della Rocco P, Hackworth C. Effects of quick rotating shift schedules on the health and adjustment of air traffic controllers. Aviat Space Environ Med 2000;71:400–407. 13. Mallis MM, DeRoshia CW. Circadian rhythms, sleep, and performance in space. Aviat Space Environ Med 2005;76:B94–B107.

Human Error 14. Reason J. Human error. Cambridge: Cambridge University Press, 1990. 15. Shappell SA, Wiegmann DA. U.S. naval aviation mishaps 1977–92: differences between single- and dual-piloted aircraft. Aviat Space Environ Med 1996;67(1):65–69. 16. Dismukes RK, Berman BA, Loukopoulos LD. The limits of expertise: rethinking pilot error and the causes of airline accidents. Aldershot: Ashgate, 2007. 17. Helmreich R, Klinect J, Merritt A. Line operations safety audit: LOSA data from US Airlines. Presentation at the Second ICAO/IATA LOSA/TEM Conference. Seattle: Boeing Training Center, 2004. 18. McDaniel MA, Einstein GO. Prospective memory: an overview and synthesis of an emerging field. Thousand Oaks: Sage, 2007.

Anthropometrics 19. Dempster WT. Space requirements of the seated operator. WADC Technical report 55–159. United States Air Force, Wright-Patterson AFB, Ohio: Wright Air Development Center, Air Research and Development Command, 1955. 20. Proctor RW, Van Zandt T. Human factors in simple and complex systems. Boston: Allyn and Bacon, 1994. 21. Gordon CC, Churchill T, Clauser CC, et al. 1987–1988 Anthropometric survey of U.S. Army personnel: summary statistics interim report. (NATICK/TR-89/027, AD A209 600). Natick: US Army Natick Research, Development and Engineering Center, 1989. 22. Robinette KM, Daanen H, Paquet E. The CAESAR project: a 3-D surface anthropometry survey in second international conference on 3-D digital imaging and modeling, 1999. IEEE Proceedings. IEEE Catalog Number: PR00062. New Brunswick, 1999:380–386. 23. Meindl RS, Hudson JA, Zehner GF. A multivariate anthropometric method for crew station design. (Publication No.: AL-TR-19930054). Wright-Patterson AFB, Ohio: AL/CFHD, 1993. 24. Hendy KC. Air crew/cockpit compatibility: a multivariate problem seeking a multivariate solution. AGARD Conference Proceedings No. 491, 1990. 25. Albery CB, Bjorn VS, Schulz RB. A comparison of human and ejection seat test manikin static centers of gravity and moments of inertia. SAFE J 1998;28(1):17–31. 26. Buhrman JR, Andries MJ, Deren M. Risk factors in ejection seat design associated with upward ejection risk for a large occupant. SAFE J 1999;29(1):29–38. 27. Albery WB, Zehner GF, Hudson JA, et al. Degradation of pilot reach under G. SAFE J 2006;34(1):1–4.

User Interfaces 28. Sanders MS, McCormick EJ, et al. Human factors in engineering and design. New York: McGraw-Hill, 1987. 29. Nielson J. Usability engineering. Cambridge: Academic Press, 1993.

Crew Resource Management 30. Helmreich RL. Managing human error in aviation. Sci Am 1997;276: 62–67. 31. ICAO. Human factors training manual. International Civil Aviation Authority (ICAO), 1998. 32. FAA. FAA advisory circular AC 120-51E Crew Resource Management. Washington, DC: Federal Aviation Administration, 2004. 33. Safety Regulation Group. CAP 737—Crew Resource Management (CRM) training guidance for flight crew, CRM Instructors (CRMIs)

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34. 35.

36.

37. 38.

39.

40.

41.

42. 43.

44.

45.

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and CRM Instructor-Examiners (CRMIEs). West Sussex: Civil Aviation Authority, 2003. NTSB. Accident investigation report NTSB-AAR-73-14. Washington, DC: National Transportation Safety Board, 1973. Cooper JE, White MD, Lauber JK. Resource management on the flight deck. (NASA Conference Publication 2120, NTIS No. N80-22083). Moffat Field: National Aeronautics and Space Administration—Ames Research Center, 1979. Helmreich RL, Foushee HC. Why Crew Resource Management? Empirical and theoretical bases of human factors training in aviation. In: Weiner EL, Kanki B, Helmreich RL, eds. Cockpit Resource Management. San Diego: Academic Press, 1993:3–45. Wiener EL, Kanki BG, Helmreich RL. Cockpit Resource Management. San Diego: Academic Press,1993. Orasanu J. Shared mental models and crew performance. 34th Annual Meeting of the Human Factors and Ergonomics Society. Orlando, Florida: Human Factors and Ergonomics Society, 1990. Klinect JR, Wilhelm John A, Helmreich RL. Threat and error management: data from line operations safety audits. In: Jensen R, Cox B, Callister J, et al. eds. The tenth international symposium on aviation psychology. Vol. 2. Columbus, Ohio: The Ohio State University, 1999:683–688. Salas E, Fowlkes JE, Stout RJ, et al. Does CRM training improve teamwork skills in the cockpit? Two evaluation studies. Hum Factors 1999;41(2):326–343. Salas E, Wilson KA, Burke CS, et al. Does Crew Resource Management training work? An update, an extension, and some critical needs. Hum Factors 2006;48(2):392–412. Helmreich RL. Managing human error in aviation. Sci Am 1997;276:40–45. Gregorich SE, Helmreich RL, Wilhelm JA, et al. Personality based clusters as predictors of aviator attitudes and performance. Proceedings of the 5th international symposium on aviation psychology. Vol. 2. Columbus: Ohio State University, 1989:686–691. Helmreich RL, Wilhelm JA, Gregorich SE, et al. Preliminary results from the evaluation of cockpit resource management training: performance ratings of flight crews. Aviat Space Environ Med 1990;61(6):576–579. Chidester TR, Helmreich RL, Gregorich SE, et al. Pilot personality and crew coordination: implications for training and selection. Int J Aviat Psychol 1991;1(1):25–44.

Unmanned Aircraft Systems 46. Tvaryanas AP, Thompson WT, Constable SH, et al. Human factors in remotely piloted aircraft operations: HFACS analysis of 221 mishaps over 10 years. Aviat Space Environ Med 2006;77(7):724–732. 47. Tvaryanas AP. Human systems integration in remotely piloted aircraft operations. Aviat Space Environ Med 2006;77:1278–1282. 48. Weeks JL. Unmanned aerial vehicle operator qualifications. Mesa: Air Force Research Laboratories, Mar 2000.Report No.: AFRL-HEAZ-TR-2000-0002. 49. Williams KW. Unmanned aircraft pilot medical and certification requirements. Oklahoma City: Civil Aerospace Medical Institute, Federal Aviation Administration, Feb 2007. Report No.: DOT/FAA/AM-07/3. 50. Barnes MJ, Knapp BG, Tillman BW, et al. Crew systems analysis of unmanned aerial vehicle (UAV) future job and tasking environments. Aberdeen Proving Ground: Army Research Laboratory, Jan 2000. Report No.: ARL-TR-2081. 51. Biggerstaff S, Blower DJ, Portman CA, et al. The development and initial validation of the unmanned aerial vehicle (UAV) external pilot selection system. Pensacola: Naval Aerospace Medical Research Laboratory, Aug 1998. Report No.: NAMRL-1398.

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52. Schreiber BT, Lyon DR, Martin EL, et al. Impact of prior flight experience on learning Predator UAV operator skills. Mesa: Air Force Research Laboratory, Feb 2002. Report No.: AFRL-HE-AZ-TR2002-0026. 53. Hall EM, Tirre WC. USAF air vehicle operator training requirements study. Mesa: Air Force Research Laboratory, Feb 1998. Report No.: AFRL-HE-BR-SR-1998-0001. 54. Tvaryanas AP. The development of empirically-based medical standards for large and weaponized unmanned aircraft system pilots. Brooks City-Base: United States Air Force, 311th Human Systems Wing, Oct 2006. Report No.: HSW-PE-BR-TR-2006-0004. 55. Tvaryanas AP. Visual scan patterns during simulated control of an uninhabited aerial vehicle. Aviat Space Environ Med 2004;75(6): 531–538. 56. McCarley JS, Wickens CD. Human factors implications of UAVs in the national airspace. Atlantic City: Federal Aviation Administration, Department of Transportation, Apr 2005. Report No.: AHFD-05-05/FAA-05-01. 57. Pope AT, Bogart EH. Identification of hazardous awareness states in monitoring environments. SAE 1992 Transactions. J Aerosp 1992;101:448–457. 58. Tvaryanas AP, Lopez N, Hickey P, et al. Effects of shift work and sustained operations: operator performance in remotely piloted aircraft (OP-REPAIR). Brooks City-Base: United States Air Force, 311th Human Systems Wing, Jan 2006. Report No.: HSW-PE-BR-TR2006-0001. 59. Barnes MJ, Matz MF. Crew simulations for unmanned aerial vehicle (UAV) applications: sustained effects, shift factors, interface issues, and crew size. Proceedings of the Human Factors and Ergonomics Society 42nd Annual Meeting. Santa Monica, Chicago: Human Factors and Ergonomics Society, Oct 5–9 1998. 60. Della Rocco P, Cruz C, Clemens JA. The role of shift work and fatigue in air traffic control operational errors and incidents. Oklahoma City: Civil Aerospace Medical Institute, Federal Aviation Administration, Jan 1999. Report No.: DOT/FAA/AM-99/2). 61. Kidd JS, Kinkade RG. Operator change-over effects in a complex task. Wright-Patterson AFB, Ohio: USAF Wright Air Development Center, Aug 1959. Report No.: WADC TR 59–235. 62. Wickens CD, Dixon S. Workload demands of remotely piloted vehicle supervision and control: single vehicle performance. UrbanaChampaign: University of Illinois, Aviation Research Lab, Sep 2002. Report No.: AHFD-02-10/MAD-02-1. 63. United States Air Force. The U.S. Air Force remotely piloted aircraft and unmanned aerial vehicle strategic vision. Retrieved from the World Wide Web: http://www.uavforum.com/library/usaf uav strategic vision.pdf, (accessed July 17 2006). 64. Tvaryanas AP, Thompson WT. Fatigue in military aviation shift workers: survey results for selected occupational groups. Aviat Space Environ Med 2006;77:1166–1170. 65. Walters BA, Huber S, French J, et al. Using simulation models to analyze the effects of crew size and crew fatigue on the control of tactical unmanned aerial vehicles (TUAVs). Aberdeen Proving Ground: Army Research Laboratory, Jul 2002. Report No.: ARL-CR0483.

Summary 66. Chapanis A. Human factors in systems engineering. New York: John Wiley & Sons, 1996. 67. Norman DA. The design of everyday things. New York: Basic Books, 2002. 68. Konz S, Johnson S. Work design: industrial ergonomics, 5th ed. Scottsdale: Holcomb Hathaway, 2000. 69. Wickens CD. Engineering psychology and human performance, 2nd ed. New York: HarperCollins Publishers, 1992.

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24

Space Operations Richard T. Jennings, Charles F. Sawin, and Michael R. Barratt

Somewhere, something incredible is waiting to be known. —Carl Sagan

Humans have explored space for 46 years, and the effects of short- and long-term microgravity exposure on human physiology have been well documented (1,2). Humans have adapted well to spaceflight, yet physiologic decrements occur during exposure to microgravity, resulting in operational constraints for short-term space missions, and necessitate countermeasures and rehabilitation for longer missions. Many of the countermeasures have not been fully protective, yet consume valuable crew time and impact microgravity-based material science investigations. Fundamental decisions remain whether the currently envisioned countermeasures are adequate to protect and maintain crewmember productivity, safety, and return-toEarth capability on exploration-class missions. There is an imperative that human microgravity research continue on the International Space Station (ISS), because the decision regarding a requirement for artificial gravity (AG) or shortarm centrifuge capability for long-duration exploration will ultimately drive spacecraft hardware requirements. The increasing number of flights and crewmembers exposed to spaceflight has allowed much better characterization of relevant medical problems seen on orbit. Medical systems, flightcrew equipment, diagnostic hardware, and treatment capabilities have evolved to reflect the growing spaceflight experience base and include current terrestrial medical thinking. Although the same spaceflight environmental considerations remain, such as microgravity, acceleration, radiation, and altered atmospheric pressure, the nominal spacecraft environment is a shirtsleeve environment and the acceleration profiles are moderate. Additional information on acceleration can be found in Chapter 4. The current medical emphasis has shifted from survival issues to problems associated with extravehicular activity (EVA), radiation, episodic illnesses, isolation, physiologic deconditioning, performance 516

optimization, and remote medical care. However, the chance for equipment failure and contingency situations outside nominal operational parameters requires adequate protective countermeasures and emergency response capabilities. The medical operations factors for space shuttle flights, ISS crews, and exploration-class missions to the Moon or Mars are quite unique. This chapter will review the relevant human physiologic data obtained during 40 years of microgravity research plus examine the current process of astronaut selection, preventive medical care, and episodic health care delivery. Following these reviews, the medical operations programs for space shuttle, ISS, and explorationclass missions will be considered.

HUMAN PHYSIOLOGY OF SPACEFLIGHT Cardiopulmonary Physiology Concerns regarding possible changes in cardiopulmonary physiology have been focused on maintenance of orthostatic function and physical work capacity. Orthostatic function is of concern during entry and landing. Maintenance of adequate physical work capacity is important for on-orbit activities as well as potential emergency egress during landing. Pulmonary changes per se have not been very notable. Gravity affects the mechanical properties of the lung and chest wall, and changes have been reported in microgravity. Early studies in Skylab suggested that vital capacity (VC) was reduced by approximately 10% during sustained spaceflight (1). Reduced VC may have resulted from the low environmental pressure of 258 mm Hg or the slightly oxygen-enriched atmosphere (partial pressure of oxygen 170 mm Hg). A 4% reduction in forced vital capacity (FVC) was also seen in 1 G under similar environmental conditions. Pulmonary

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517

3.0

PAC/hr

Preflight

Inflight

Postflight

2.0

1.0 0.0 0.3

PVC/hr

function was examined during shuttle research missions; peak expiratory flow rate, compared with preflight standing values, was reduced by 12.5% on flight day 2 (FD2) but returned to normal by FD9 (3). FVC and forced expired volume in 1 second (FEV1 ) were slightly reduced on FD2 but returned to normal by FD5 and were slightly increased by FD9. Analysis of the maximum expiratory flow-volume curve showed that microgravity caused no consistent change in the curve configuration when individual in-flight days were compared with preflight standing curves. The reduction in FVC and FEV1 during the early phase of exposure is probably due to an increase in intrathoracic blood volume caused by the cephalad shift of body fluids. In summary, no physiologically significant changes in pulmonary function have been observed during spaceflight to date. Obtaining valid data during flight activities is more complex than in the normal research laboratory environment. Changes in diet, sleep patterns, exercise, medications, and fluid intake before and during spaceflight missions are difficult to control. Safety restrictions may make many standard research protocols inadvisable. Data collections must occur without disruption of primary mission objectives. Hardware malfunctions during in-flight data collections affect the quantity and/or quality of results. Over the last three decades, symptoms of cardiovascular changes have ranged from postflight orthostatic tachycardia and decreased exercise capacity to serious cardiac rhythm disturbances. The most documented symptom of cardiovascular dysfunction, postflight orthostatic intolerance, has affected a significant percentage of U.S. astronauts (25% for short duration missions and up to 80% for Shuttle-Mir astronauts). A basic parameter, heart rate, had previously been reported as increased, decreased, or unchanged during spaceflight. This important information deficit was corrected through systematic studies of Holter monitoring, blood pressure measurements, and related assessments of dysrhythmias, cardiac function, and orthostatic intolerance (Figure 24-1). In a related descriptive study, 32 astronauts were evaluated with two-dimensional, directed M-mode echocardiography to determine the effects of spaceflight on cardiac volume, cardiac function, and cardiac mass. In a more operationally oriented study, 34 astronauts were instrumented with an automatic blood pressure/heart rate monitor that would permit data acquisition while the crewmembers wore their launch and entry suits (LES). The following parameters were obtained: heart rate; systolic, diastolic, and mean arterial pressure; and pulse pressure. Several important findings resulted from these descriptive studies. First, it was shown that heart rate, diastolic pressure, and their variabilities were reduced during spaceflight (4). Second, the diurnal variations of both heart rate and diastolic pressure were reduced during spaceflight. Third, monitoring records demonstrated that short-duration spaceflight did not increase dysrhythmias. Echocardiographic data showed some minor, statistically significant changes. Ejection fraction and velocity of circumferential fiber shortening did not change significantly, suggesting that spaceflight of this duration has no effect on

S PA C E O P E R AT I O N S

0.2 0.1 0.0 −10

−5

Early

Late

.+2

FIGURE 24-1 Premature atrial contraction (PAC) and premature ventricular contraction (PVC) occurrence. (Reprinted from Fritch-Yelle JM, Charles JB, Crockett MJ, et al. Microgravity decreases heart rate and arterial pressure in humans. J Appl Physiol 1996;80:910–914; with permission.)

myocardial contractility. Left ventricular wall thickness and myocardial mass index also showed no significant changes. Standing upright for the first time after landing is associated with a significant decrease in systolic pressure. In several instances, the decrease was greater than 20 mm Hg. This occurred in 22% of the subjects on landing day, but did not occur in any subjects before flight (2). Therefore, this observed decrease in systolic pressure reflects the cardiovascular response of individuals adapted to shortduration microgravity. Many subjects used a pressurized anti-G suit during landing to support cardiovascular function. The recommended minimum inflation pressure for this protective garment was 26 mm Hg or 0.5 lb per square inch guage (psig). Most subjects inflated the suit to 52 mm Hg; this counterpressure would largely offset the hydrostatic column effect of standing in a normal gravity environment. Diastolic pressure was more adequately maintained in those who inflated their anti-G suits. There was a 70% increase in heart rate upon standing compared with the increase seen before flight. The mean standing heart rate was 120 beats/min, but a maximum of 160 beats/min was observed in one stressed crewmember. An important cardiovascular study focused on an integrated assessment of orthostatic function (2). There were 29 participants, and 8 could not complete a 10-minute stand test on landing day because they became presyncopal (2). These subjects displayed arterial pressure and heart rate responses to standing that were similar to those seen in adrenergic failure. On landing day, their standing norepinephrine levels were significantly lower than the norepinephrine levels of the astronauts who did not become presyncopal. Plasma volumes (PVs) were not significantly different between the two groups. The group that became presyncopal on landing day had lower preflight supine and standing diastolic

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pressures and lower peripheral vascular resistance than the nonpresyncopal group. These data taken as a whole provide convincing evidence that the precipitating factor for orthostatic intolerance after spaceflight was a hypoadrenergic response to orthostatic stress. The parallel insufficient levels of plasma norepinephrine, diastolic pressure, and peripheral vascular resistance strongly support this. Removal of all hydrostatic gradients when entering microgravity of spaceflight produces a large headward fluid shift; this has been commonly observed and is reflected in measurements of decreased leg volume and observations of an edematous face. This fluid shift is believed to be the primary stimulus for many of the physiologic effects of spaceflight, including a reduced PV and, ultimately, orthostatic intolerance on return to Earth’s gravity. It has been hypothesized that central venous pressure (CVP) would increase due to the headward fluid shift encountered upon entering microgravity. Direct measurements were made by catheter, and the results were somewhat surprising: CVP was 8.4 cm H2 O seated before flight; 15 cm H2 O in the supine legs-elevated posture before launch in the shuttle; and 2.5 cm H2 O after 10 minutes in space (5). A corollary measurement of left ventricular enddiastolic dimension measured by echocardiography showed an increase from a mean of 4.6 cm supine preflight to 5.0 cm within 48 hours in space. Other investigators have evaluated the cardiovascular response to submaximal exercise in spaceflight (6). Cardiac output, heart rate, blood pressure, and oxygen consumption were measured repeatedly both at rest and at exercise levels approximating 30% and 60% preflight maximum. Cardiac output at rest in-flight was an average 1.5 L/min greater than erect preflight, but not different from supine preflight values. Inflight resting heart rate was an average 15 beats/min lower than the erect control value and 5 beats/min lower than the supine control value. Inflight stroke volume was elevated relative to both erect and supine control values. Inflight mean arterial blood pressure was 6 mm Hg less than erect control values, but not different from supine control values. In spaceflight, the increase in cardiac output with oxygen consumption was due entirely to an increase in heart rate. Stroke volume was not a linear function of oxygen consumption. Total peripheral resistance in-flight at rest was lower than that erect preflight but not different from that supine. One of the mechanisms responsible may have been hydrostatic unloading of dependent veins. The subjects were able to exercise in microgravity until they achieved their control maximal heart rate and maximal oxygen consumption. Mean cardiac power, expressed as the product of cardiac output and mean arterial pressure (triple product) does not appear to be a limiting factor in the increase of cardiac output with increasing levels of exercise in-flight. The maximal stroke volume seen in-flight occurred at rest; stroke volume actually declined with increasing oxygen consumption (6). Cardiovascular countermeasure studies were conducted to determine if early inflation of the standard five-bladder anti-G suit before centrifuge simulation of shuttle landing would provide better protection against orthostasis than the

standard symptomatic inflation regimen (2). Preinflation to at least 0.5 psig protected eye-level blood pressures better and resulted in lower maximum heart rates during these simulations. Although preinflation subjects exhibited a greater decrease in systolic pressure during centrifugation (–51 mm Hg vs. −36 mm Hg), they completed the runs with higher absolute systolic pressures. These findings resulted in a flight rule that now requires preinflation of anti-G suits before reentry. The National Aeronautics and Space Administration (NASA) evaluated a liquid cooling garment (LCG) as a countermeasure to the thermal load imposed by the LES. This thermal load was believed to be largely responsible for the increased incidence of orthostatic intolerance (∼25% preChallenger and 52% post-Challenger) noted following their introduction as standard garments following the Challenger accident in January 1986. The metabolic heat produced by an average astronaut is approximately 100 W/hr. Before use of the LCG, body heat could be dissipated only by circulating cabin air across the chest within the LES garment. This provided modest benefit in a cool cabin and no benefit after landing when cabin air temperatures often reached 27◦ C to 32◦ C. The LCG uses a thermoelectric cooler to chill water before circulating it through a full-torso, tube-filled garment. The LCG is presently worn under the new advanced crew escape suit (ACES) for launch and landing; it has proved extremely effective both for general comfort and orthostatic protection. Weight loss postflight averaged 0.7 kg less for crewmembers who wore the LCG. This difference probably represented decreased water loss due to lower sweat rates and respiratory loss during entry and landing activities. The frequency of orthostatic symptoms has decreased to pre-Challenger levels. Alternative fluid loads were evaluated because the standard 8 g of sodium chloride diluted to be approximately isotonic in a liter of water evoked nausea and emesis in many subjects, which in turn led to decreased compliance with the flight rule requiring fluid loading before entry. Ground-based studies determined that isotonic fluids were essential. Either isotonic consomm´e or Astroade (potassium citrate instead of sodium chloride) was equally beneficial. Fluid loads containing natural sugars were not as effective because they induced diuresis. Hypertonic solutions often caused diarrhea. Therefore, the standard fluid load is now an isotonic fluid, 15 mL/kg preflight body weight, taken 2 hours before landing. Experience gained during shuttle operations raised significant concerns regarding orthostatic tolerance for crewmembers returning from 4- to 6-month missions on Mir. Soyuz vehicles return their cosmonauts in the supine position with the G-load from chest to back (positive Gx ). If a normally seated astronaut or cosmonaut were to become orthostatically intolerant during entry and shuttle landing, there could be an approximate 15-minute period when no assistance would be possible. Therefore, a decision was made to use a conservative approach and return long-duration crew in the supine posture until sufficient experience had

CHAPTER 24

been gained to determine that this would not be necessary. NASA designed, manufactured, and provided the recumbent seating system (RSS) for use on Shuttle/Mir missions. Its use has been extended to the ISS for returning longduration crews (missions longer than 30 days). This system accommodates up to three crewmembers in the shuttle mid-deck. It was first used for the STS-71/Mir 18 mission to return one astronaut and two cosmonauts from their 115-day mission. Each subject also wore an anti-G suit that was inflated to the nominal pressure of 75 mm Hg (1.5 psi). Heart rates were approximately 25 beats/min lower than those for seated shuttle crewmembers on previous missions. Upon first standing, the crew from Mir demonstrated comparable heart rates to those from the earlier, significantly shorter shuttle missions. Systolic and diastolic blood pressures were slightly lower in the Mir crew relative to shuttle crews. These two findings indicate the protective benefit of the countermeasure. The fact that upon first standing the two groups displayed similar cardiovascular responses is encouraging; it indicates that the general cardiovascular status of the returning Mir crew was comparable with that of shuttle crewmembers. Exercise physiology was studied because it was recognized that both physical and psychological benefits were received from in-flight exercise sessions. These investigations resulted in establishment of a flight rule requiring exercise on missions greater than 10 days in duration. A key objective was to determine the optimal combination of a crewmember’s fitness before flight and in-flight countermeasures that would result in minimal performance decrements. Conducting wellcontrolled investigations proved extremely difficult due to multiple conflicting priorities during each mission. In general, moderate to more intense levels of cycle exercise resulted in improved submaximal exercise responses after flight. This response required exercising more than three times per week for greater than 20 minutes per session at intensities of 60% to 80% preflight maximum work loads (2) (Figure 24-2).

Preflight Landing

4.0 −4.5% 3.5

VO2 (L/min)

3.0

−21.8%

2.5

−19.2% −27.1%

2.0 1.5 1.0 1

2

3

EVA only

Group

FIGURE 24-2

Aerobic capacity. EVA, extravehicular activity.

S PA C E O P E R AT I O N S

519

One suggested countermeasure, based on ground-based bed rest studies, required a single bout of maximal, cycle exercise 24 hours before landing. This was postulated to improve post–flight aerobic exercise response and orthostatic tolerance. Results from the initial subjects did not support the hypothesis, and further trials were canceled (2). Significant additional effort is still required to define an optimal exercise program that gives consideration to aerobic versus resistive; upper body versus lower body; eccentric (force while lengthening) versus concentric (force while shortening); high-intensity interval versus low-intensity continuous protocols; and high impact versus low impact. This information is required to determine an appropriate balance of crew risk and discomfort versus the expected physiologic benefit of the exercise.

Neurovestibular Physiology A significant concern for operational spaceflight is the occurrence of space motion sickness (SMS). Attempts in the Russian space program to prevent SMS by selecting individuals with a high tolerance to vestibular simulation have not been successful. Applicants to the astronaut corps are not screened for motion sickness resistance. Moreover, among crewmembers who have completed preflight Coriolis testing, no correlation has been found between test tolerance and susceptibility to SMS. SMS occurs typically during the initial 3 days of spaceflight. No single drug or combination of drugs has been proved to protect all people. Promethazine, the most effective of the antihistamines, has proved very effective when taken by intramuscular injection or as a suppository. An injection of 25 to 50 mg of promethazine is now the recommended treatment for moderate to severe SMS in the U.S. space program (7,8). In summary, results obtained in both the U.S. and Russian space programs indicate that most spacecrews will experience some symptoms of SMS (>70%), and that these symptoms are brought on or made worse by head movements. These symptoms may be debilitating, and their probability of occurrence has led to operational rules that preclude EVA during the first 3 mission days. All but two cosmonauts following long flights and 27% after short flights showed symptoms on the first and second days after landing, and sometimes on the next few days as well, that could be classified as clinical vestibular dysfunctions. These symptoms consisted of illusions (e.g., dizziness, illusory movement of self or surroundings), motor reactions (e.g., pointing errors), and vestibular reactions (e.g., nystagmus of central or sometimes peripheral nature), which varied in severity. On the first day after landing, all cosmonauts complained of instability upon standing and of ‘‘swaying’’ from side to side while walking (9). Flight surgeons (FSs) frequently observed disequilibrium in crewmembers during the first few hours after spaceflight. These observations were in large part attributed to functional changes in the neurovestibular system. Four primary research goals to investigate the neurovestibular system were (a) to establish a normative database of vestibular and associated sensory changes in response to spaceflight, (b) to

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determine the underlying etiology of neurovestibular and sensory-motor changes associated with exposure to microgravity and the subsequent return to Earth, (c) to provide immediate feedback to spaceflight crews regarding potential countermeasures that could improve performance and safety during and after fight, and (d) to design appropriate countermeasures that could be implemented for future missions. The neural processes that mediate human spatial orientation and the sensory rearrangement encountered during orbital flight are optimally studied through second- and third-order responses. The following parameters were measured during separate studies: (a) eye movements during acquisition of either static or moving visual targets; (b) postural and locomotor responses provoked by unexpected movement of the support surface, changes in the interaction of visual, proprioceptive, and vestibular information, changes in the major postural muscles through descending pathways, or changes in locomotor pathways; and (c) verbal reports of perceived self-orientation and self-motion that enhance and complement conclusions drawn from the analysis of oculomotor, postural, and locomotor responses. Spatial orientation in this context is defined as situational awareness, where a crewmember’s perception of attitude, position, or motion of the spacecraft or other objects in three-dimensional space, including orientation of one’s own body, is different from actual physical events. The interaction of stimuli and responses is illustrated in Figure 24-3 (2). Perception of spatial orientation is determined by integrating information from several sensory modalities. This

STIMULI

VISUAL STIMULI Static and moving visual targets

RESPONSES

Cerebral cortex

SENSATIONS Motion, visual illusions, and spatial orientation of body and/or spacecraft

Ocular muscles

MOTION STIMULI Angular about X, Y, and Z body axes. Concommitant linear acceleration in X and Y axes during pitch and roll acceleration, changes in the inertial gravitational stimuli

FIGURE 24-3

Brain

Retina

Superior colliculus

PASSIVE VOLUNTARY OR COMPENSATORY MOVEMENT Hear/body movement or movement of the support surface

involves higher levels of processing within the central nervous system to control eye movements, stabilize locomotion, and maintain posture. Operational problems occur when reflex responses to perceived spatial orientation lead to inappropriate compensatory actions. Future application of effective countermeasures depends, in large part, on the interpretation of results from appropriate neuroscience investigations. A number of experimental paradigms, classified as voluntary head movements (VHMs), included the performance of (a) target acquisition, (b) gaze stabilization, (c) pursuit tracking, and (d) sinusoidal head oscillations. Target acquisition protocols used a cruciform tangent system where targets were permanently fixed at predictable angular distances in both the horizontal and vertical planes. To facilitate differentiation, each target was color coded (e.g., ±20 degrees green; ±30 degrees red, etc.) corresponding with the degree of angular offset from center. The subject was required to use a time optimal strategy for all target acquisition tasks, and to look from the central fixation point to a specified target indicated by the operator (e.g., right red, left green, up blue, etc.) as quickly and accurately as possible using both head and eye movement to acquire the target. During flight, measurements were obtained using a cruciform target display that attached to the shuttle mid-deck lockers. In all cases, surface electrodes on the face enabled quantifying eye movements that were obtained with both horizontal and vertical electrooculography. Head movements were detected with a triaxial rate sensor system mounted on goggles that

Oculomotor nuclei

Cerebellum

Autonomic centers

EYE MOVEMENTS Vestibulo-ocular reflex dynamics, optokinetic responses, visual stabilization, smooth pursuit, head/eye dynamics, and visualvestibular interaction SYMPTOMS OF MOTION SICKNESS

Semicircular canals Vestibular nuclei Otoliths SPINAL AND PERIPHERAL NERVOUS SYSTEM Neck and postural musculature

Central nervous system responses.

POSTURE Measurement of biomechanics, segmental coordination, electromyography LOCOMOTION Spatial orientation Measurement of eye-headtrunk coordination, lower limb kinetics, lower limb muscle activation patterns

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521

in maintaining gaze. Significant difficulties were observed postflight, including multiple saccades (2) (Figure 24-4). Consequently, the time required to clearly focus an image of the target on the retina increased by as much as 1 to 1.5 seconds relative to preflight times. This important finding led to discussions with shuttle commanders suggesting that they limit in particular their vertical head movements to monitor instruments during approach and landing. Spatial orientation was tested in several ways. First, it was of interest to determine whether in space the brain is able to detect objects moving at a constant velocity as opposed to those moving at constant linear acceleration. It was found that subjects are able to successfully change their strategy catching falling objects in space. They apparently predict the velocity of the ball and also its momentum, and make an upward hand movement to catch the ball. Hand-eye coordination was tested in reaching, pointing, and grasping tasks. Amplitude, reaction time, duration, and velocity were studied while reaching for an X-Y position without seeing the hand. The amplitude of the movements was the same on earth as in-flight, but there was a slight increase in reaction time and duration, and a decrease in velocity. Two protocols investigating postural stability were performed by 40 crewmembers before, during, and after shuttle missions of varying duration. These tests used a clinical Neurocom posture platform to challenge the subject’s ability to maintain balance by six different sequential tests. The first of these protocols focused primarily on reactive responses by quantifying the reflex (open-loop) response to sudden stability-threatening perturbations of base support. The second protocol focused on sensory integration by quantifying the postural sway during quiet upright stance with normal, reduced, and altered sensory feedback. After flight, tests began on landing day, as soon after the shuttle wheels stopped as possible, and were scheduled on an approximately logarithmic time scale during the subsequent 8 days (Figure 24-5).

Preflight Gaze Head

Eye

20° 1 sec

Postflight (R+0) Gaze Eye

Head

FIGURE 24-4

S PA C E O P E R AT I O N S

Saccades.

were fixed firmly to the head. Both head movements (using a head-mounted laser) and eye movements were calibrated. Pursuit tracking, (i.e., visually moving from a central focal point to illuminated targets) was performed before flight and after flight, using two separate protocols: (a) smooth pursuit by the eyes only, and (b) pursuit tracking with the head and eyes together. In addition, a modification of these protocols used predictable, sinusoidal stimuli and unpredictable stimuli with randomly directed velocity steps. The objective was to study smooth pursuit eye movement and to evaluate its interaction with the vestibuloocular reflex. The sinusoidal pursuit tracking tasks were performed at moderate (0.33 Hz) and high (1.4 Hz) frequencies to investigate the relative contributions of eye and head movement

Normalized score

1.2

1.0

5th percentile

0.8

Score = 1.04 − 0.17 e−0.2t − 0.09 e−0.01t (n = 30) 0.6 0

FIGURE 24-5

Balance control recovery.

50

100

150

Time after landing (hour)

200

250

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The effect of spaceflight on neural control of posture was inferred from differences between preflight and postflight performance in all subjects. The effect of mission duration was inferred from statistical comparison between the performance of subjects on short-, medium-, and long-duration missions. The effect of previous spaceflight experience was inferred from statistical comparison between the performance of the rookie and veteran fliers. Astronauts with previous flight experience demonstrated better postural stability that suggested retained neurosensory learning. Centrifugation in microgravity produces linear accelerations that mimic the pull of gravity. On Earth, subjects feel tilted to the side during centrifugation that produces linear acceleration along an interaural axis, and tilted back during centrifugation when lying on their backs. This is attributable to the sum of the upward gravitational linear acceleration with the centripetal acceleration from centrifugation. On landing, there was enhanced perception of tilt. Oculomotor measures of otolith-ocular reflexes, such as ocular counterrolling, were similar before, during, and after flight. Spatial orientation to the vestibuloocular reflex in response to centripetal linear acceleration appeared to be maintained throughout the flight. These findings demonstrate that there is a strongly developed sense of orientation to gravity that persists in space (10).

Bone and Muscle Physiology Bone and muscle respond to microgravity within the first few days of a space mission. In space, the mechanical load, or amount of weight that bones must support, is reduced almost to zero. At the same time, many bones that aid in movement are no longer used as intensely as they are on Earth. These characteristics of life in microgravity evoke two of the biggest concerns regarding the human body during spaceflight: disuse osteoporosis and muscle atrophy. Bones are relieved of mechanical loads normally experienced on Earth, and calcium normally stored in bones (which gives bones strength) is broken down and released into the bloodstream. This decrease in density, or bone mass, is called disuse osteoporosis. The exact mechanism by which the body divests itself of bone mass is still unknown. Current theories point to the fact that in space, old bone is absorbed much faster than new bone is laid down. The changes in bone density begin within the first few days in space. The most severe loss occurs between the second and fifth months in space, although the process appears to continue throughout the entire stay in microgravity. Bone demineralization is tracked during a mission by monitoring electrolytes; calcium in the urine serves as one marker of bone loss. Baseline bone mineral density, bone loss, and recovery are monitored preand postflight through imaging techniques such as dualenergy x-ray absorptiometry (DEXA). These measurements have documented losses in the lower spine and hip, posterior elements of the vertebrae, femoral neck, and tibia. Recovery of bone mass may take up to 2 years despite the fact that excess calcium no longer appears in urine soon after return to Earth. The risk of injury to long-duration flight crews is compounded by coordination and balance difficulties

typically experienced upon return to Earth. The potential for falling and fracturing a bone is much higher than normal following flight, especially in those with a lower bone mass and reduced fracture threshold. As bone mass is lost in microgravity, muscle undergoes a similar process. Numerous studies throughout the history of spaceflight have documented changes to muscle mass and architecture. In essence, the muscles used in standing, walking, and posture maintenance on Earth are relatively unused in space. These muscles begin to atrophy, becoming smaller and weaker. As a result, astronauts may lose strength and size in their muscles, ultimately extending the time for recovery of bone mass. Again, the exact mechanism behind this change remains elusive. Bone loss in spaceflight is much more accelerated than bone loss on Earth. Gender differences in spaceflight are also less pronounced than on Earth; in space, both men and women lose bone mineral at approximately the same rate. The human musculoskeletal system is a complex, multicomponent array of effector organs (including muscles), connectors (such as tendons and ligaments), and structural components (bones) responsible for the support and movement of the human body. The skeletal system provides the mechanical support to which muscles attach for movement, protects the internal organs, houses the bone marrow, and stores calcium, phosphorous, and other ions. The skeleton allows us to remain upright and move in the presence of gravity. In the presence of gravity, our bipedal stance and gait dictate that certain bone and muscle groups are essential to posture and movement. The muscles of the legs and trunk are responsible for producing the forces required for activities such as walking, running, and maintenance of an upright posture in a terrestrial setting. In contrast, arm bones and muscles are responsible for providing the forces required for activities associated with upper body balance and manual dexterity. Consequently, the functioning of bone and muscle are closely linked. It is therefore not surprising that environmental conditions affecting bone impact muscle as well. Bone is a highly vascular, constantly changing, specialized type of mineralized connective tissue consisting of two types of bone cells. Osteoblasts, cells that lay down new bone material, are responsible for bone formation, whereas the osteoclasts reabsorb old bone material. Formation and destruction of bone is an ongoing process throughout life; we typically replace approximately 20% of our bone each year. The loss of bone in space appears to be related to an adaptive process where the body senses it does not need as much bone as when it was on the ground. The hormonal regulation of calcium and bone metabolism reflects this change. At the cellular level, the decreased calcium absorption is related to decreases in circulating vitamin D. Researchers have also observed that decreases in certain hormonal levels (e.g., growth-stimulating hormone that affects the parathyroid gland) correlate with decreased bone formation. Generally accepted theory holds that our endocrine system responds to microgravity by disrupting the balance between bone resorption and bone construction, such that resorption

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exceeds construction. In addition, it is assumed that genetic factors also play a role in determining the extent to which bone is lost during weightlessness. Scientists have extensively evaluated the minerals that provide bones with their strength. Calcium is the primary mineral required for strong bones, so researchers have studied the amount of calcium in the body and its movement throughout the body. The excretion of calcium and phosphorous during spaceflight is increased. The rate of calcium loss from bone increases during flight. The rate of bone calcium loss is approximately 250 mg/d, which calculates to 1% to 2% mass loss per month in the lower extremities. Recovery after spaceflight is approximately 100 mg/d; therefore, the recovery of lost bone mass will take approximately 2.5 times as long as the mission duration. NASA researchers scanned the bones of 19 Russian cosmonauts who flew between 126 and 312 days on the Mir space station. Bone loss in the spine (>1% per month) exceeded that seen in bed rest subjects. Decreases in bending and torsional strength, averaging approximately 8% in the femoral neck and approximately 4.5% in the femoral shaft, also were measured. Together, these data suggest that countermeasures for maintenance of bone integrity were inadequate. Changes in bone mineral density after astronauts participated in 4- to 6-month flights on the Mir space station are shown in Figure 24-6. Density of the skeleton was measured within the first week following flight. Mean loss was −11% in the trochanter area of the femur, −6% in the neck of the femur, −7% in the calcaneus of the heel, −7% in the pelvis, and −1% in the lumbar spine. It was documented that lumbar spine losses continued postflight for up to 6 months as other regions recovered. Final recovery to preflight density occurred for five of seven subjects. Aerobic and to some degree resistive

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exercises have been the primary countermeasures against bone loss throughout the history of spaceflight, but they have been only partially effective. Although the Skylab-3 and Skylab-4 crews as well as the Mir crews performed extensive aerobic exercise during flight, they showed substantial mineral losses (1). This has cast doubt on the effectiveness of the exercise program. Additional, intensive resistive exercise programs are under evaluation. New countermeasures will likely include resistive exercise directed at specific affected areas, and possibly AG. Resistive exercise is difficult to accomplish in space, and AG requires major spacecraft hardware considerations. Potential pharmacologic countermeasures are based on a class of drugs referred to as bisphosphonates; these drugs block the action of osteoclasts and are currently under investigation in bed rest studies (Figure 24-7). The link between bone loss and muscle atrophy is widely accepted. The absence of mechanical strain on the lower limbs during spaceflight leads to a rapid decline in muscle mass. This decrease in muscle mass and strength appears to be a contributing factor to bone loss in space. The exact mechanism of these muscular effects on bone is unknown. There are indications of alterations in molecules used by the body to transmit information about a change in mechanical strain. For example, studies have demonstrated that levels of interleukins and insulin-like growth factor I decrease in microgravity and therefore enhance bone resorption. Microgravity also promotes enhanced absorption of calcium directly from bone, which further affects hormonal levels. It is possible that specific cells in the bone marrow may promote the formation of bone-resorbing osteoclasts. In addition, bone loss is thought to be progressive; the amount of bone loss in weight-bearing bones seems proportional to the length of flight. Unfortunately, bone loss occurs despite

Bone mass density Femur neck 0

Femur trochanter L1–L4 spine

Change from baseline (%)

Calcaneus Pelvis −4

−8

−12 R+5d

FIGURE 24-6

Bone mass density.

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R + 3–6 m

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FIGURE 24-7 Senator John H. Glenn, Jr. pictured with the osteoporosis experiment in orbit (OSTEO) (photo courtesy National Aeronautics and Space Administration).

available countermeasures. It is projected that the loss will stop after some time, but we have yet to reach that point in the flight studies to date. Mammalian skeletal muscle has a standard architecture developed around the contractile protein elements responsible for force production, namely actin and myosin. It is the actin-myosin ‘‘molecular engine’’ that is responsible for producing the force developed during muscle contraction. The actual process of movement is accomplished through muscle contraction. Contraction is the result of a complex chemical reaction. When movement is needed, the brain releases a neurotransmitter that communicates an electrical impulse to the muscle fiber. Thousands of fibers contract to produce movement in the muscle. This process—from the time that the signal leaves the brain to the time that the muscle contracts—takes only minutes. Movement may also be the consequence of a reflex action. In this case, the brain is not part of the signal pathway; the spinal cord is the natural connection between a reflex action and movement of the muscle. All muscles are slightly contracted during consciousness; this is referred to as tonus. Tonus contributes to the upright posture and keeps the muscles stimulated and healthy. Nonstimulation leads to muscle atrophy. Slowtwitch fibers are those normally associated with activities requiring endurance, such as long distance running, walking, or maintenance of posture. Fast-twitch fibers are those associated with muscle normally used for rapid movement

such as sprinting or power lifting. One of the most important aspects of muscle physiology with regard to environmental challenges is the level and the type of mechanical load to which a particular muscle is exposed. Muscles adapt based on their loading histories. To better understand changes in muscle, researchers developed a breakthrough methodology to directly measure proteins involved in muscle synthesis. Direct measurement of protein synthesis rates in astronauts suggests that the normal balance maintained between protein synthesis and degradation is disturbed during spaceflight. Protein degradation rates must be significantly increased during spaceflight in order to account for the rapid loss of the muscle mass. Pre- and postflight imaging has shown dramatic reductions in skeletal muscle volume in a large number of muscle groups, including the soleus/gastrocnemius (calf muscle), hamstrings, and quadriceps (thigh) muscles after both short- (8 days) and long-duration (115 days) spaceflight. Reductions in both lean body mass and muscle volume are paralleled by a concomitant decrease in the cross-sectional area of the individual muscle fibers. Limited data, obtained from muscle biopsy from both American astronauts and Russian cosmonauts, show a reduction in muscle fiber with associated loss of contractile protein elements, actin and myosin. In addition, the loss of muscle mass is most prevalent in the antigravity muscles and is associated with a loss of muscle strength and endurance (2). There is no doubt that the removal of mechanical load from the musculoskeletal

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system is the most important initiating factor in skeletal muscle atrophy. Changes in muscle morphology were studied by pre- and postflight biopsy of the vastus lateralis muscle in the thigh. Significant changes were evident after 6- to 9-day shuttle missions, including a 15% reduction in the cross-sectional area of type 1 and a 22% reduction in cross-sectional area of type 2 muscle fibers. Decreased capillary density and increased ratio of glycolytic/oxidative enzymes resulted in muscle becoming relatively more anaerobic. Muscle function was measured by a Lido dynamometer. Large decrements in trunk flexor and extensor strength, both concentric and eccentric, and significant losses in concentric quadriceps extension were seen. Muscle strength typically recovered within 7 to 10 days, with the exception of concentric back extension following short-duration missions (2).

Hematology Astronauts consistently return from space with a decreased red blood cell mass (RBCM) (11). This has been observed during Apollo missions with a 258 mm Hg (5 psia) oxygen atmospheric pressure, during Skylab with a normal sea-level oxygen partial pressure but lower total pressure environment (BP = 258 mm Hg), and finally in shuttle missions where the atmospheric composition and pressure were sea-level equivalent. During detailed studies on Spacelab missions, the observed decrease in RBCM was attributed to fewer new red blood cells (RBCs) being released from the bone marrow (11). The hematocrit, reflecting changes in the RBC count and mean corpuscular volume (MCV), did not increase significantly during flight. Six days after flight, RBC count, hemoglobin concentration, and hematocrit were all below preflight mean values. The mechanisms of action are thought to occur as follows. PV decreases, causing an increase in hemoglobin concentration that affects a decrease in erythropoietin or other growth factors or cytokines. The RBCM decreases by destruction of recently formed RBCs to a level appropriate for the microgravity environment. This represents normal adaptation to microgravity. On return to Earth, there is acute hypovolemia as vascular space dependent on gravity is refilled, an increase in PV, a decrease in hemoglobin concentration (representing ‘‘anemia’’), and an increase in serum erythropoietin. Because erythropoietin is either decreased or normal in-flight, it supports the thesis that decreased RBCM is a normal adaptation to the microgravity environment. Changes after return to Earth, that is, orthostatic hypotension, rapid increase in PV, and increase in serum erythropoietin indicate that the optimal values for both plasma and RBCs are greater on Earth than in space. Normal RBC survival was documented by use of circulating chromium-tagged RBCs. Typically 1% of RBCs is replaced daily. The increase in chromium-specific activity and decrease in RBCM probably occurred as a consequence of not replacing cells that were normally destroyed. Detailed studies of blood volume were not accomplished for the astronauts who flew 4- to 6-month missions on the Russian Mir station. However, interesting mean changes were measured pre- to postflight that were generally consistent

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with prior observations for other programs. Hemoglobin was decreased approximately 10% postflight. Hematocrit was decreased 4%, and the RBC count was down approximately 6%. There was no apparent change in MCV.

Fluid and Electrolyte Balance Water diuresis was expected to occur early in-flight but was not observed in Skylab crews. Osmolality of the urine formed was higher than that of plasma, averaging 300 mOsm higher than preflight. Generally, 24-hour urine volumes indicated that crewmembers excreted volumes similar to their preflight control values. Plasma sodium was generally decreased throughout the flight, and potassium demonstrated a trend toward becoming slightly though not statistically significantly elevated. The loss in potassium was also demonstrated by decreased total body exchangeable potassium. There was an increased aldosterone secretion that probably caused the potassium loss. Slight increases were observed in plasma creatinine, indicative of slight decreases in creatinine clearance. In turn, this may reflect minor alterations in renal function in-flight. Calcium and phosphorous levels were significantly elevated in the plasma as in the urine throughout the inflight and early postflight phase. Urinary epinephrine level was generally normal or decreased in-flight and elevated postflight. Norepinephrine was more variable but did show periods of increase during the flight and significant increases post flight. It is well established that epinephrine is most often associated with anxiety responses whereas norepinephrine is more closely related to physical stress. The in-flight norepinephrine levels are probably the reflection of the high levels of physical exercise undertaken by the crewmembers. In summary, although significant biochemical changes were observed, they varied in magnitude and direction, and all disappeared shortly after return to Earth. Fluid and electrolyte balance, renal function, calcium balance, and energy utilization are all affected by spaceflight, although clinically important alterations are rarely observed. For the most part, these changes are thought to be indicative of successful adaptation of the body to the combined stresses of weightlessness; the human body seems to adapt so successfully to the weightless environment that return to gravity on Earth causes more concern than living in space (1).

Nutrition Skylab was a prototype space station flown in the early 1970s. There were three missions, Skylab-2, -3, and -4, with three astronauts each and lasting 28, 59, and 84 days, respectively. For each of the three Skylab missions, a metabolic balance study was performed beginning at least 21 days preflight and continuing until 17 days after return for the nine astronauts. Variables monitored included diet, fluid, and electrolyte balance, various hormones, and nitrogen balance. The Skylab investigators found that the protein loss was greatest during the first month, but continued for the duration of the mission (1).

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These Skylab data for the first 12 days were compared with studies conducted on 1- to 2-week Shuttle missions (12). There was no statistically significant difference in the preflight dietary intake or estimated nitrogen balance between the two groups, although there may have been a trend for nitrogen balance to be less for the shuttle astronauts. Although energy intake was higher on Skylab, the nitrogen loss was greater. Over the entire duration of the Skylab missions, urinary nitrogen excretion was increased by 3.1 g/d above the preflight control period. With the shuttle, the decreased nitrogen balance paralleled the decreased protein intake (12). Therefore, it is clear that energy intake and nitrogen balance were different between shuttle and Skylab, and when the estimated nitrogen balance is used as the criterion for comparison, shuttle crews fared better. Skylab astronauts individually developed a prescribed daily exercise regimen, which increased in intensity from Skylab-2 through Skylab-4. This daily exercise regimen was not required or prescribed. Each crewmember selected his own mix of equipment utilization and specific protocols with advice from ground monitors. For Skylab-2, only a cycle ergometer was available; for Skylab-3, an apparatus referred to as a mini-gym that provided some resistive exercise was added. A simulated treadmill was added for Skylab-4. This device was a Tefloncoated metal plate that the subject slid his stocking-covered feet across while maintaining position with a bungee cord restraint harness designed for the ergometer. It was uncertain how the combined effects of limited physical activity and perhaps increased stress would affect nutritional requirements. Earlier spaceflight studies indicated changes in protein turnover that were consistent with a stress reaction during shuttle flights. Estimated water turnover (important inflight due to concerns about the potential for renal stone formation) was a by-product of the nutritional studies. Various experts have recommended inflight water intake of at least 2,500 mL/d. Rehydrated food and fruit drinks provide approximately 80% of this fluid intake. Energy expenditure requirements were determined for 13 male astronauts 36 to 51 years of age during spaceflights 8 to 14 days in duration (2). Methods used were developed from the doubly labeled water (DLW) technique modified to account for baseline isotopic differences associated with the shuttle potable water system. The analytic uncertainty of the DLW method performed in ground-based laboratories is ±4.5% actual average metabolic rate. The slightly higher isotopic doses used for these studies reduced the uncertainty to approximately ±3.5%. Baseline metabolic studies were accomplished approximately 2 months before flight, whereas flight studies typically began on the third flight day to avoid confounding effects associated with SMS. The energy requirements associated with physical activity in microgravity were largely unknown, and the relatively close confines of the spacecraft tend to limit the extent of physical activity. Ambient temperature and relative humidity are held relatively constant within the shuttle at 21◦ C to 24◦ C and 20% to 30%, respectively. During flight, energy intake (8.8 ± 2.3 MJ/day) was less than flight

total energy expenditure (11.7 ± 1.9 MJ/day; p 10 g/d) diet during their missions. Total fluid intake from foods and liquids was approximately 2 L/d or less. Crewmembers ‘‘fluid loaded’’ approximately 90 minutes before landing by ingesting a liter of physiologic saline. Statistically significant changes were shown for pH, calcium, and citrate in the direction of increased stoneforming risk (2) (Table 24-1). Urinary citrate, a known inhibitor of renal stone formation, was lower after spaceflight (575 ± 31 mg/d) relative to before flight (707 ± 33 mg/d, p